Another case is doing something technologically simple enough that benefits from having a fully customized workflow outweigh having to write some stuff by yours

Another case is doing something technologically simple enough that benefits from having a fully customized workflow outweigh having to write some stuff by yourself. This can happen with content-heavy genres like, say, 2D point'n'clicks - you don't get much by using an existing engine there, but you have to follow its idiosyncrasies which may or may not work well for you and your team.