For me I tend to go about 50/50 with my posts about my doggy girls. 50% is about our relationship or things about them that are non-sexual. The other 50% does relate to sex in one form or another, whether it be about what sex with them is like, or whether it be able how my doggy girls consent to sex, etc.
But this is an adult (18+) website with porn on it, and to top it all off it's about a HIGHLY taboo subject in society. It makes sense that a lot of people will want to talk about sex, as it's something you just cannot talk about elsewhere, and it's one of the key separating difference between us and your typical "absolutely loves their pets" animal owner. Yeah legitimate zoos are heavily outnumbered by the "leg humpers" and fetishists 10:1, but even for that 10% that are zoos it makes sense that they'll want to talk about sex.