Have they killed many paid products?

I think there is justified wariness about building too much on top of any service given away for free.

Explain all the businesses built on YouTube, then. YT is "free" to most consumers (paid for by ads), but there are literally people who make their livings as YouTube personalities.

What's to explain? All the people who chose not to do this, because it didn't seem like a safe enough business model?

Right, they choose to do it on top of a Google-run service they don’t pay for. According to you, this shouldn’t be happening.

No, read it again. According to me, many people are unwilling to build a life on sand, it weighs negatively in their choices. The fact that some are observed to take the gamble proves nothing. (And the fact that some of those got nasty surprises of being de-monetized proves that they should have been concerned.)