UI frameworks are a tool which allows programmers to focus on designing a website rather than stressing about urls. I think that UI frameworks are a necessity in modern web development, as creating everything from scratch would be a huge waste of time. By learning UI frameworks, developers are able to spend there time improving a websites user interface, instead of worrying too much about the clunky aspects of HTML.
HTML as a language can be repetitive, and at times frustrating to format. By using UI elements whose behaviour is more user friendly, we can make UI’s much better with much less work. In addition, these sites are often more visually appealing, as a result of them being formatted better.
In short UI frameworks are great tools which allow developers to streamline their design process. UI frameworks are great for faster, higher quality development.