It is definitely not never. I for example occasionally post some new content. And there are definitely people who sometimes post new content.
But there are many reasons why making porn just is not worth it.
1. Anything interesting you post here is swiftly stolen or even claimed by someone else and shared onto absolute shit sites like z18x where it is served next to literal animal abuse.
2. The amount of effort that goes into producing a well made piece of content is absolutely not met with an adequate amount of recognition. This means that the risks and disadvantages far outweigh the benefits.
3. Zoo is illegal almost everywhere and if viewing porn is not, then making porn almost always is. So making porn puts you and your animals in quite a bit of danger. This amount of danger grew up compared to the past. Nowadays it is more easy to identify authors. You have to pay more attention to detail. Which is in my opinion the reason why porn got made more in the past.
New crap commercial content is made, from what I have seen leaked, and except for visual quality is almost entirely equal in all other aspects to old content. Equal amount of mistreatment of animals, dildogging, wrong techniques, over exaggeration and the other nonsense you can expect from commercial porn producers. Maybe with the exception of less fake cum.
New zoophile content is also made but much less since it gets even less recognition from other people. Most users who watch zoo porn are not zoophiles after all and watch porn to see women do weird things with something that maybe is a dog but more importantly there is a woman in the same frame.
Commercially made zoophile content is extremely prone to turning into crap content since as soon as you take money, you have customers to please and standards slip.
This makes making good zoophile porn harder and even less worth the effort.