Limiting the number of provider is exactly the point. You either pay the developers or make your code available.

I don't know about Elastic, but redis was accepting contributions so changing the license was very controversial, if not legally questionable. AFAIK mongodb, like sqlite, don't accept contributions.

Big lucrative deal? Just buy a license, like tens of thousands of others do, millions if we include other "code available" products that also offer licenses: red hat, Ubuntu, temporal, different Kafka versions, Postgres, MySQL, etc.