No, making YouTube free, and then deciding 15 years later to adjust the policy for ads is not 'illegal'.

The amount of narrative promoting here on HN is distressing.

Google does some nice things, some not so much nice things.

Because they adjust their advertising policy doesn't make them either illegal actors or pariahs.

There's no evidence indication that this is 'predatory pricing'.

Again - if there is an issue, it's with their ownership of Search, Mobile towards prioritizing other products.