Even for trivial SPAs it's often easier to roll the basic functionality yourself. Flipping over to something like Angular introduces technical and cognitive overhead that often isn't worth the trouble for something simple.
The huge frontend frameworks have an upfront learning cost and tend to be unfortunately leaky abstractions, but they're still much easier to maintain than a jQuery/JS mess with a bunch of DOM-manipulation code and HTML strings living right next to the business logic. They at least force the code into an understandable architecture and separate the view from business concerns. Experienced developers know how to structure their frontend JS already, but novice ones--the same ones that would feel the pain of learning a framework/ecosystem on top of JS when they first try to pick it up for an SPA--almost certainly won't.
Remember, they don't know which part of the framework you are using or not, or which parts are important or not, so even if you are using it for one little thing, they probably have to learn most of it to understand how it interacts. Since so many frameworks overload standard functionality, it is impossible to know how a framework interacts with your code until you know all of these things.
Using 20 frameworks is about as efficient use of your time as having one you built yourself. The sweet spot for a medium-sized application is using 2-4 (maybe a few more if they are really standard or do really specialized functionality - i.e., a PDF library) for the most critical components, and still maintaining the remaining quirks yourself.
So, for example, Ruby-on-Rails + Bootstrap + JQuery goes a very long way, and doesn't put an undue burden on people trying to get to know your code.
If your application become sufficiently complex that it can't be easily grokked by a decent dev, that's when you know it's time to switch.
Until then it's just over engineering (which the JS community admittedly loves).
Guy A believes his custom design is simple enough to comprehend by anyone. Guy B doesn't agree.
It doesn't really matter at the end of the day. If you work in a team environment, the toolset will be pre-determined already. You don't have a choice.
