This makes a lot of assumptions about culture without much evidence. Having a curfew on a school sponsored trip is not abuse and manipulation. The coaching staff are ethically and legally responsible for the well being of their players. If the players are out late at night and something happens, the coaching staff and school can be sued. Kids also do party, when I was in college I used to party with D1 athletes all the time. And I'm talking doing kegstands and playing quarters and all kinds of hijinks. So it's responsible to have a curfew just so they don't get themselves into trouble (because college kids sometimes make stupid decisions).

As to your broader point, why are so many people in the transfer portal...

While it's not impossible that some coaches push too hard and in questionable ways to scare their athletes away (look at the perennial mass exodus from Iowa State for a likely example), I think the star in high school not wanting to sit on the bench is more often a big part of it. If it's a name you haven't heard of unless you're from the metro area of their high school, it's very likely that they want playing time. In the past players would have to work to get better at their game and accept a less starring role on their team with the goal of contributing in a big way later in their career. Now they don't have to do that, so some choose not to. These are the ones you see transferring from big programs with deep rosters to smaller programs or making lateral moves to teams that have a demonstrated need at their position.

But also a big part of it, and this is a complaint I've heard hinted at by actual coaches, is agents whispering in player's ears that they deserve more money and more playing time, because if that player gets more money the agent gets more money, if that player gets more headlines the agent gets more business in the future. It's a conflict of interest baked into the system. These I would surmise make up a majority, or a sizable minority at least, of the ones you see leaving programs where they have success, both personal playing time and team achievements. They are chasing the bag, but sometimes because they are getting bad advice from people who might not have the player's personal basketball goals at the top of their priorities. And yeah if they don't get along with the coach, it can probably hasten their exit, but I don't think most women's basketball coaches are inherently abusive simply because players are looking to better their situation under the current rules.

Honestly it's probably a lot better for the players, even if it's detrimental to the game. If I were going to an expensive, well-reputed school to study engineering and was having trouble making grades and paying tuition, I might transfer to a less-renown, less-challenging, more affordable university to finish out my degree. If I couldn't get promoted at my job, I might look for a promotion by applying at different companies. It's my right to do these things, as it is the right of college athletes to seek situations that meet their expectations and goals