Developers are creating lots of UI libraries but after sometime they lose traction and support for this library abandoned, bug fixes/improvements will be halted. If so, why create so many libraries instead of writing yet another theme for bootstrap. Best example is material ui kits, they are a lot, but only 2 or 3 of them are still continuing development
While I agree with the sentiment in general, I don't think Bootstrap is a great solution either. It's very easy for a project to outgrow Bootstrap at which point it becomes a burden instead of an asset.
I'm not OP and I made the experience with Zurb's Foundation but the problem isn't specific to the framework.
In my opinion you'll run into issues with these kitchen sink frameworks once you try to do something custom - customizing elements and components feels like fighting the framework at a certain point and once you realize that it's hard to get out.
I don't recommend using Bootstrap or any other framework unless you're very certain about future requirements.
I find that using the SCSS/Less source for bootstrap is less fighting... the layout/structure is pretty easy to use internally, for the most part, everything I need for creating additional controls starts from variables and utilities.
But you would break all that once it comes to updating the framework, wouldn't you? With Foundation it was either that or constantly overriding framework defaults. Once you took a look at the rules in the browser inspector / dev tools you saw many of them leading to conflicts and it felt very messy despite end results working out.
I usually copy the variables/utils to my project (often just the variables)... when updating minor/point version updates, it's usually a quick diff against the framework version to see what's been added/changed. Major versions are usually close to a rewrite of the rendering templates/components, so that's the case regardless.
I have my own bootstrap.scss, with my own variables/utils... the rest point to the framework versions... It's pretty easy to do and works out really well imho. Of course, I often only change a few colors, and tweak some of the font defaults.
