Predation, disease, and extinction-level suffering afflicted animals for hundreds of millions of years before humans existed to sin — since animal suffering long predates any human moral failure, it cannot be blamed on the Fall, which leaves God directly responsible for designing a system of staggering non-human suffering with no clear redemptive purpose.

Why people find it persuasive

The fossil record shows predation, parasitism, and mass extinction going back over 500 million years, long before Homo sapiens; an omnipotent God who could have designed any biological system chose instead one saturated with suffering for creatures incapable of moral wrongdoing, moral growth, or free response to God — none of the standard human-directed theodicies (soul-building, free will, moral responsibility) even apply to a trilobite or a struggling gazelle.

Important distinctions

• • Human moral evil requiring human free will vs. animal suffering, which requires a different kind of explanation.
• • A literal historical Fall causally retroactive across all of natural history vs. a Fall (or cosmic disorder) with effects understood non-chronologically or cosmically rather than strictly causally-temporally prior.
• • Suffering as intrinsically, exhaustively bad with zero possible justifying role vs. suffering as an integrated part of a functioning, value-generating biological and ecological system.
• • Animal experience of pain (nociception) vs. the kind of self-aware, existentially freighted suffering that afflicts reflective human beings.

Christian response

• • Not all theodicies are anthropocentric: several serious explanations for natural evil target the value of a law-governed, stable, predictable natural order as such (a world operating by consistent natural laws, including the laws of biology and ecology that make evolution, ecosystems, and even the emergence of moral agents like humans possible, requires a cosmos where energy transfer, death, and the food chain function according to reliable regularities) — a world where God constantly, miraculously intervened to prevent every instance of animal suffering would be a fundamentally different, arguably less coherent and less genuinely law-governed kind of universe, and it's not obvious such intervention-heavy alternative would actually be better on net rather than simply differently structured, with its own likely costs (unpredictability undermining the very possibility of creaturely agency, scientific reasoning, and long-term ecological stability).
• • The intensity and moral significance of animal suffering is also plausibly overstated by a straightforward extrapolation from human suffering: there is serious, ongoing scientific and philosophical debate (not merely apologetic special pleading) about the degree to which most animals, especially those without complex central nervous systems comparable to vertebrates' higher cognitive structures, experience suffering with the self-aware, temporally-extended, existentially dreadful quality distinctive of human suffering, versus a more limited, momentary nociceptive response without the same reflective, anticipatory, or narrative dimension that makes human suffering so morally weighty — this doesn't eliminate the moral weight of animal suffering, especially for cognitively sophisticated animals (mammals, birds), but it does complicate simple appeals to '500 million years of suffering' as if it were straightforwardly comparable in kind to human suffering across the entire animal kingdom.
• • On the theological side, some contemporary Christian thinkers (e.g., Michael Murray in 'Nature Red in Tooth and Claw') argue the Fall's effects, whatever their precise metaphysical mechanism, need not be understood as strictly causally-temporally sequential (human sin causing changes retroactively backward through millions of years of prior fossil history in linear time) but rather that the entire created order, viewed by God from outside ordinary temporal sequence, was subjected to disorder and 'futility' (Romans 8:20-22, which explicitly speaks of the whole creation, not just humanity, groaning and being subjected to futility, awaiting future redemption) as part of a single, integrated divine plan encompassing the whole scope of a good-but-fallen cosmos, not requiring a strict linear chronological causal chain from a historical human sin backward into deep time.
• • Others (theistic evolutionists like Christopher Southgate, in 'The Groaning of Creation') offer a genuinely different, non-Fall-based theodicy: that an evolutionary process operating by natural selection is very plausibly the only, or at least the most efficient and elegant, means available to produce the extraordinary diversity, complexity, and eventual emergence of moral agents capable of relationship with God, such that some real measure of struggle, death, and suffering is not a corruption of an originally different plan but a necessary feature of the particular good (immense biological creativity and diversity, culminating in creatures capable of love and moral response) that this kind of world uniquely makes possible — while still affirming, per Romans 8, that this suffering is temporary, taken seriously by God, and ultimately to be redeemed and healed in the new creation, not the final word.
• • Whatever explanatory model one adopts, it's worth noting the Christian tradition does not treat animal suffering as something God is indifferent to or has no answer for — Romans 8's cosmic redemption language explicitly includes non-human creation in the scope of final restoration ('the creation itself will be set free from its bondage to corruption'), which at minimum shows animal suffering is taken with theological seriousness within the tradition's own eschatological hope, not simply dismissed as irrelevant collateral damage to a human-only redemptive story.

Christian counterresponse

This is honestly among the harder items in the theodicy literature, and serious Christian philosophers (Southgate explicitly, for instance) concede that no full theodicy fully dissolves the cost, offering instead what he calls a 'theodicy of adequate response' — an account that doesn't claim to show the suffering was strictly necessary in some airtight logical sense (since we cannot access all possible alternative creation-designs God might have compared and rejected, nor establish that a suffering-free alternative achieving comparably rich value was genuinely available) but argues that the goods actually achieved (evolutionary creativity, ecological richness, ultimately embodied moral agents) are real and substantial, that God is understood to fully identify with and enter into creaturely suffering (via the incarnation and cross, extending even to non-human suffering by extension of the same divine compassion), and that final eschatological redemption of all creation (not merely human souls) is offered as a genuine, promised answer rather than mere resignation to unredeemed cost.