If it was that simple, Google would have been the obvious choice. They have already started migrating to GCP and signed an $800 million dollar three year deal.
Yes. It's made THEM billions of dollars. If you've ever been on the other side of the pipeline, as an advertiser or a web site owner, you know you're treated as a statistic. Businesses suddenly disappear when Google delists them on either end. That's most visible on Youtube, where random Youtubers find themselves demonatized with no apparent rhyme, reason, or appeal, but it happens all over the Googleyweb.
If it's one of a dozen places you advertise, that's fine. If you're trying to run a business where it's a core platform, you quickly run into the limits there.