Is it really a financial liability part really pushing companies for these policies? I never heard this argument before and compared to salaries PTO is minuscule liability...

Seems much more likely companies just trying to squeeze employees into taking less PTO.

Pretty much every article on a naive Google search lists "reduced financial liability" as one of the corporate benefits. Even the ones that talk about more complicated financial scenarios deal with "unexpectedly short-staffed" rather than, "We have a big financial liability on our books."

A somewhat random example:

https://www.higginbotham.com/blog/unlimited-pto-pros-cons/

"Cost efficiency. Traditional PTO policies can result in financial liabilities due to unused vacation payouts when employees leave the company. With unlimited PTO, these liabilities are eliminated. This can be particularly advantageous for companies looking to manage their finances more effectively."