I think there was a company (might have been Virgin?) that did unlimited holiday, but the issue was that people ended up feeling ashamed for taking holiday and so basically ended up taking less than if they were given 25 days holiday.

My last contract had that and the first year I barely used 2 weeks. My regional manager started giving us heads up during contract negotiation time that we might not get it. Ended up taking 3 weeks that he approved and felt so good to actually use the benefits that were promised. He was going to retire soon anyways, so he was approving left and right.

Ended up get hired back at the same place under a different company, and now our PTO and vacation is horseshit

I generally agree with you but my last two jobs transitioned to unlimited while I was there and the amount of time I took off was not impacted at either. Both of these jobs were client focused billable time types of jobs so I do think that has something to do with it, as long as I'm hitting my billable targets and contribution goals they don't care how much time I have off really. I once took December off at the end of a super busy year.

If you set a minimum vacation time, it's not bad. But most places don't do that, because they know you'll take less time if they say unlimited.

My company is pretty lax, where I live you're entitled to 20 days paid leave by law but a contractor in my team had unlimited leave and made good use of it, she would travel pretty frequently, but she would still meet all her deadlines so management were fine with it