I can absolutely see why Denise Crosby quit the show. Tasha had basically no personality and only the three things we really know about her is that she grew up on an anarchic planet with rape gangs, she has a sister in a resistance group on that planet who she abandoned, and she fucked Data. That's pretty much it.
I'm honestly amazed any women stuck around with Rick Berman in charge. Michelle Forbes had a lot of stuff going on pre- and post- Star Trek, so I definitely don't blame her for sticking around. Poor Denise Crosby has not had that big of a career.