Have you ever wondered why we keep re-developing the exact features all over again? There is plenty of free snippets on the Internet and we could just use them. But we don't do it! – Why?
I think there is a gap between a static code snippet and the way we code modern UI. Our goal is to make it reactive and maintainable. And, some may say that you can organise your jQuery and global CSS well. – Fine, but it requires a lot of self-discipline to keep it organised and we humans make mistakes. Under pressure we are willing to break the rules. To turn the static snippet to work in your framework, you need to convert HTML to your templating language, scope CSS and turn JS into app actions. It's a lot of work! Often, it's easier to start from scratch.
That's one of the reasons I've been developing a simplified online frontend web dev environment. I'll let you judge whether it's helpful by your self. Just watch this video where I convert a contact form I found on CodePen into reactive UI:
Let me know what you think about the presented prototype.