If you want a TL;DR: here it is!
This essay will be on the shorter end because UI Frameworks are relatively straightforward with a proportionately steep learning curve. However, frameworks are worth the time learning due to how consistent, efficient, and ample things are. With pre-made components and assets for reuse at your leisure, it is a better alternative than making them over and over again.
Frameworks, such as Bootstrap 5, allow for webpage developers to create the UI front-end of a webpage using intuitive systems (note how I didn’t say “simple”). From columns and rows, components like navigation bars, headers, and footers, one would think things are rainbows and sunshine on the other side of the fence.
But no.
Its own classes and components brings new syntax, and organization system requires understanding if you desire to replicate or convert existing HTML into a framework-compatible format. This, combined with the already complex (in my opinion) system that CSS and HTML is, it is no wonder that there exists a learning curve when dealing with frameworks.
But that is not to say that there are indeed many reasons why people use frameworks:
The elements that frameworks bring allow for consistency across a project, so that instead of having to fine-tune a custom component and then copy-pasting it around, you can simply call a pre-existing component or a series of components in their own containers/columns/rows: ensuring that edits in the long run don’t devolve into headaches.
The grid system as well allows for creating webpages for various layouts easily without the hassle of wrapping your skull around the specific dimensions and resolutions in HTML. Bootstrap 5, especially, exceeds in this regard with many ways to section off and position elements across a displayed webpage.
Both of these reasons also help make an efficient and responsive system that is perfect for working collaboratively. The universalized system and easy-to-read syntax helps with maintaining and comprehending code and what needs to be done. This makes frameworks a perfect reflection of the principles of software engineering, where the process of designing and engineering trumps the reasons for avoiding frameworks in the first place.
“Why not put in more work now to make things easier in the long run?”
I absolutely abhor anything related to HTML and CSS. Suffering and all that having to create webpages. The only joy I derive is making it function, not making it look pretty. So when I learned of frameworks that provided a way to simply create functioning UI, and an actually presentable website without having to delve too deep into custom HTML and CSS, I was ready to dive in with no hesitation.
However, that is not to say that there are no consequences of using frameworks. For one, dedicating time to learning how the Bootstrap 5 system works in the first place and all the classes and such is like learning a whole different language. Secondly, if you are converting pre-existing projects into a new framework, or a framework at all, then there’s a lot of clean up and reworking to be done before any satisfactory results occur.
(This second problem might just be the reason why some people decide to stay away from using frameworks for the time being)
But, if I ever find myself developing webpages, then I’m for sure using something like Bootstrap 5 to help pretty up my page instead of having to manually set the margins and columns myself.