You are reinventing the wheel, slowing yourself down and making maintenance more difficult by creating everything from scratch everytime. I think that's common sense among developers.
That's exactly how everyone else develops (but using open-source libraries): use a module system and glue together things from previous successful projects (made by other people). Why your own private framework is better than what is out there is a whole different matter.
And, btw, it's not private. Most of my code is on github. I just don't try to force it down others' throats.
Picking up bits and pieces from old code isn't a framework. Its a specific tool. Think of Backbone or Ember or Angular as a mechanic shop. Things work a very certain way. The copy and paste code from other sites is a hammer, or wrench. You don't have to use them a certain way, but when you have them, you can use how they are intended.
Unless it solves a specific problem you have, not using any framework will almost always mean more bugs, brittle code, a less consistent API, lots of documentation effort (or lack of) and a much larger learning curve for people other than yourself.
Not to mention that these frameworks undergo alot more extensive testing than an average developers code will ever go through. By using a framework you benefit from not having to go through the pain of dealing with all the different browser models and quirks that every version introduces or takes away.
For really advanced or incredibly high performance tasks you might be correct but to me that is the 1% of tasks, for everything else a framework should give you all the scaffolding you need allowing you to instead focus on tasks that add real value into the product/service you are working on.
What I don't do is make intrusive assumptions about the entirety of your application's architecture simply because you include my one little focused tool.
This is particularly what I value in open source frameworks - the hundreds, thousands, tens of thousands, maybe even million of man-hours that have gone into debugging edge cases, cross-browserifying, and finding security holes, stuff I would never be able to replicate on my own in any reasonable time frame. Especially the latter, given the security situation on the internet these days.
My SOP is, stand on the shoulders of giants, unless there's a particular requirement that precludes doing so. Such requirements are rare, most client work actively benefits from use of a framework.