This has always struck me as a pretty juicy deal going for the corporation. They get N years of "next level" work out of you while still being able to pay those N years in "previous level" salary. Good deal for them.
How ridiculous the opposite sounds: You pay me at the next level for 3 years, and only then I'll know you're serious and will start working at that level. You'd get laughed out of the room. But the company has this exact deal in reverse.
It's not really that juicy for the corp. If they hire (promote) you without experience, they are hiring someone without experience for a position and then have to go and hire again to replace someone else. Vs. just hiring someone with experience
Ed Snowden revealed that these companies share their data with the US government:
https://www.theguardian.com/world/2013/jun/06/us-tech-giants...
also, even you think about using it "their own uses" - much of that is scrutinizing you to make you better susceptible to ads and other solicitations by their paying clients. I mean, people are not the clients of Google and Meta - they're the raw material.