A- They do it on purpose because it distracts players or messes with timing. It works. It wins them points.
B- The phenomenon got worse over time. In the beginning people thought it was cute/sign-of-effort/not-a-big-deal/turn-on. By the time Sharapova started doing her multi-tonal shrieking it was an established part of women's tennis.
C- Do mainstream fans of women's tennis fans complain about it? i doubt this is the case. Commentators don't count. They just use it for filler in their conversations.
D- No one will/should do anything about it unless the non-shrieker players complain about it. They won't because they're too afraid of looking weak in front of their fans/opponents.
Solution: Teasing and ridicule go a long way in lending moral support against the practice. Not watching women's tennis can help with symptoms. Who wants to watch tennis on mute without hearing the ball?
Disclaimer: I'm NOT a coach...
Real tennis: https://www.youtube.com/watch?v=yDqnkLJ9BtM