If you are interested, I did a live recording of building a blog from scratch [1]. From the content, to a decent framework to run it. This is more of a purpose oriented framework where you build the features you need.
[1]: https://idiallo.com/video/website-from-scratch-part-1-conten...
The 'framework' of your app is a collection of patterns and interfaces that allow you to implement your actual features as easily as possible. Whether you get that by importing 2M loc from the same source, piecing together tiny libraries that do one thing well, or write the entire thing from scratch, it's the same result.
I'd agree with you if I was using the definition everyone else is, which seems to only cover the fist case (importing a shitload of code from one place).
Using any pre-made library is a trade-off where you incur some technical debt in return for up-front speed. This is obvious if you look at the extremes (i.e if you have infinite time then I'm 100% sure that using Django isn't the optimal way to build your app, and if you're writing your own framework then by definition you're spending a bunch of time writing code that doesn't directly implement features. Everything else is somewhere in-between).
If you've written a framework that you can just sub in across multiple projects, then it falls victim to the same trade-off you'd have to take with an existing framework. Unless there's something about your framework that's straight up better for the general use case than existing frameworks (in which case well done, but "just build something better than Django/React/Whatever" isn't really advice that's useful for the average dev).
I think it's far more realistic to have familiarity with a set of patterns and small libraries for solving specific problems, and when starting a new project, port over the parts which are relevant to it. I've written tons of this kind of code in my career, and I don't see any point whatsoever in releasing my own open source framework. Instead, whenever I implement something that I think is interesting or might be useful later, I build a minimal gist that implements the concept in-case I need to refer to it later and re-use the code.
I think if I had my own framework that was robust enough to just copy wholesale between projects, and I had to train all of the devs on my team to use it each time, it'd just be the worst of both worlds. I'd much rather either use something that's reasonably standardized, or piece together the right set of tools for the job and educate and familiarise everyone else with it as I go.
But that also doesn't fail mysteriously in ways that even StackOverflow can't diagnose (like all of the open source frameworks do).