Hiring actual voice actors is very expensive and nearly worthless, even if there are some from the Casting Call Club. Here are my pet peeves with them...
1.) They may not get the voice lines done, even by a specified deadline.
2.) The inflections may not fit with the dialog as expected. It feels like they would just read the given lines like a book rather than expressing the mandatory emotions.
3.) Little to no one would be interested in auditioning for the desired role.
The usage of AI applies to music, sound effects, and more. AI may be expensive to run, but it's the only way to go for an individual who can't afford to hire professional musicians, voice actors, etc.
This is not a means to replace human creativity as most people make it out to be.
It feels too much of a long story to give a definitive answer, though there is one applicable reason.
To attract not only the furry community, but also those who enjoy kinks such as weight gain predominantly.