There was an Ask an Apologist subforum some years ago. The forum was also not on Discourse then and had several paid mods that were more active than the current mods. My guess is that having apologists here, like having the paid mods here, cost money, and CA wants to limit how much it spends on this forum.
There is also the issue of stubborn posters just wanting to argue anyway (see how badly some treat the priests who post), the fact that most apologetics questions are the same ones over and over, and also frankly a lot of the threads that get posted here nowadays are not apologetics and are more along the lines of very basic questions, teenagers asking “is this a sin”, people having issues with prayers to Mary or saints, and people with agony aunt-type marital or personal situations. I can’t really see a CA apologist wanting to spend time on this version of the forum.