This blog post and the comments here are amazing. In no other software field but indie game dev does spending a year trying to build your own toolset instead of $ACTUAL_PRODUCT_THAT_MAKES_MONEY draw praise.
It's cargo-cult word-thinking. "Game engine" is associated with "game" because of the success of id Software, Epic Games, Valve, CryTek, et al. So people who don't think the way programmers do, have the impression that a game engine is a required step in the software development process to have a successful game.