It's a fidelity problem. If you restrict yourself to very simple interactions and behaviors, you can make a Twine game and get the effect you're looking for without touching code. But then your scope gets more ambitious and you want characters to be fully realized, a mobile camera, voice acting, combat simulation, and so on... and then the asset pipeline blows up into something way bigger, every interaction requires additional scripting steps, you start needing to customize the rendering code...

No one of those features stops you, but you get a "death by paper cuts" effect, because you eventually hit a mine that requires original technology to be written - most commonly, something to do with collision code. A good team led by a competent producer is able to figure out how to get the right effect within the budget, but it's never an easy process, and game productions have a habit of "pitching the moon and shipping with swiss cheese".

There are lots of frameworks for game development, but the problem is exactly in what you've described: rails. You can only get so far within the constraints of those frameworks before you need something it just can't do, and have to develop yourself. Depending on the framework, this may not even be possible (which is what leads to creation of new frameworks).

With that said, a lot of great (albeit typically somewhat simple) games are made with frameworks. When I when to a few game jams back in college, we typically started with something so that we could have a "complete" game by the end.

Also, using an existing engine often means giving up the possibility of having unique features or capabilities. Having the only game with multidimensional quad-resolution bumpmap tensors (in realtime!) can be a major selling point. Of course, in most cases, you'll get a better overall game by focusing on the art, story, gameplay, etc., but that doesn't always translate to sales.

Yes http://www.unity3d.com/ is essentially "Game on Rails". But, just as you can quickly and easily build a failed startup with Rails, Unity doesn't really save you from building a game that no one really wants.