Yep, companies give "unlimited PTO" because it's a way to actually reduce the amount of PTO employees take.
Give them 20 days PTO/year? They'll take around 20 a year.
Give them unlimited PTO? They need to justify every bit of PTO, so probably only get to take 4 or 5 for important days.
Similar to how companies are reaching to create the death machine from the book "do not create the death machine", companies are racing to create the "dead internet", where even if humanity dies, there will still be internet traffic.