Artificial semination is key to commercial animal agriculture, and that too would be unambiguously rape in human standards. Not to mention the horrific living conditions of most animals farmed for meat.

It’s really just because one has always been normal, and the other hasn’t, aka it’s cultural. It’s not rational. Though there’s also arguably far more benefit in killing for meat vs. having sex with dubious consent, so that can be a consideration that isn’t purely cultural.