I'm sorry, I accidentally deleted instead of editing, reposted above.
That is a very reasonable assumption: code that is used by a dozen projects, with a few variations for each of them, is certainly less tested than code shared by a thousand different projects and developers using a standard API. It's not inherently flawed or bad, but a matter of numbers.
Also have in mind that frameworks vary wildy. Angular and Ember might be absurdly prescriptive, you have to do things a certain way, while Backbone and others are extremely flexible, merely a collection of useful patterns and tools.
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Why do frameworks exist? They allow you to speed-up development, offer battle-hardened code, a consistent API, good documentation and proven design patterns, plus developers can make use of their previous experience with it. It's a matter of choice, and of course there are trade-offs, namely flexibility.
It's not about being "the standard", just providing useful tools. I bet you end up using a lot of the same components over and over, right? Package them up and call it the 'Getify Framework' and you're in the same spot.
I don't get why you feel that someone is 'forcing' you to do anything? You say that you write your own code because
I already understood that (architecture) domain pretty well.
I’ve done similar “single-page apps” dozens of times. I’m
getting a little better each time I do it. I learn new lessons
about easier ways to mix the pieces together with each project.
Well, guess what? That's how Backbone, Angular, and all other frameworks came to be. From other developers that decided to share their solutions, and people adopted them because they liked it and it solved some of their problems, not because they were forced to (?).