Sure, it's #3 but whole point is new installs have mostly stalled and outside companies absolutely mainlining the .Net Framework Kool-Aid, no one is building greenfield on it. I've worked for several .Net Core companies, all of them have either converted or in process of converting away from MSSQL to MySQL flavor or PostGres.

Microsoft is heavily investing in Postgres in fact which is why they bought PostGres sharding company, Citus and looking at commit history on PostGres, they have several employees actively working on it. They also contributed DocumentDB which is Mongo over Postgres.

It will take a long time to die and Microsoft will still continue to do little work on the product and stack your money in their vault while giggling.