Being able to yum/apt-get install and edit a config file or run a couple quick commands is a lot easier than needing to figure out how to feed SETUP.EXE the right arguments and deal with a mess of arcane windows CLI tools + a mix of PowerShell to configure SQL Server.

Automating the installation of PostgreSQL on Linux with ansible is a couple lines of tasks in a playbook + a template for postgresql.conf and pg_hba.conf. Automating the installation of SQL Server on Windows (as well as the installation of Windows in general if you aren't using System Center) is a huge pain in the ass.

That's enough less "care and feeding" for me.