tldr: You're probably going to have competition that's comparable skill who's willing to work 40+ hours.
What type of high skilled job are you talking about?
For my example I'll use electrical engineers. Electrical engineers go to school between 4 and 5 years for a bachelors. Yes, it's high skilled, but when you're going to your first job and they expect you to be willing to work 50 hour weeks when needed if that's a sticking point they'll find someone else that went to school that long for the high skilled but still entry level job.
Then that engineer gets 5 years experience. They're more specialized. But they still have peers that would be willing to put in 40+ hours a week. So they gotta keep it up to be competitive for promotion. They may be able to command more money for their time, but it's still hard to demand that they get to work less.
By the time that engineer gets so specialized that he can command a 32 hours week he's probably so specialized that companies don't need her around for more than 6 months to a year doing what she's specialized in for only 32 hours/week. The engineer has reached consultant level. But consultants are usually contractors that don't work for the company. Once that project is finished the consultant has to find more work that requires their niche and can handle a 32 hour work week. Even then if you want to be able to put in your contract that you only work 4 8 hour days you better be the best there is.
Or you can use nurses as an example. But there's such a shortage of nurses that entry level have to work OT or their employer won't stay in business. One of my friends is an experience nurse, but part time to her means she only works part of the year and takes long un-employed vacations when she has the money saved up. With her she's either working 40+ or not working at all.