There has been plenty of proof of illegal (downright malicious) behavior in multiple dimension by big tech (anti competitive, anti privacy, bad security practices, keeping wages low, lying in front of congress, inciting (or at least turning a blind eye on) war, genocide and riots, the list goes on...) and new revelations like these here are showing up nearly daily. Especially in the ad industry incentives are not aligned.

The problem is that fines (which is proof of their illegal actions, since you asked for proof) are always very low - so companies design their actions with that in mind.