[magduf]

>Why would someone choose SQL Server when options like Postgres or MySQL/MariaDB exist?

Because they're in an organization where they're already invested in Microsoft technologies, so it's much easier to just use MS's DB instead of something entirely different that doesn't integrate as well.

It's similar to why many people use Apple software products that aren't as good as alternatives: if you already have an Apple platform/device, it's easier and better integrated and likely already installed.

[vonseel]

Understood, but I should have prefaced my question with “for greenfield / new development”.

[magduf]

My answer is still the same, and actually assumed that. No one is really "greenfield": everyone is already invested in some technology to some extent. If your organization is already invested in MS technologies, your managers only know MS, and your developers only know MS/.NET/etc., then the choice is pretty obvious: MS SQL Server. Switching to Linux/PostgreSQL would be a sea change for an organization like that (even though, IMO, it would be better in the long run).

Similarly, if your organization is already a Linux-based one, running Linux servers for everything, adopting SQL Server would be a huge PITA and would likely be laughed out of the room if suggested.