> Didn't stop you from selling your SW for the Windows platform without paying Microsoft a dime

Microsoft would charge you up-front for things like dev tools (Visual Studio), documentation (MSDN), server software (MS SQL, Windows Server), etc. Yeah, you could get alternatives, but it wasn't until the very end of the 90s that you started to see FOSS really take off in a way that would be appropriate for an enterprise-style environment.

App stores take a cut of revenue, while Microsoft would get its revenue before your project shipped.