It's a risk / reward thing, if getting fined for less than what they earned (both in actual money and in removing competition from the equation) then it's worth the risk.
You forgot to state the follow up: these fines require changes, and lacking changes get higher very quickly. Losing 1/3 of you advertisement-market is not profitable either if it gets to that.
Just because they are larger than US doesn’t mean they are extremely large - I would argue it’s US fines that are too small, and regulators being too mild.
As for larger ever US fine - perhaps for Google. US can also be rough.