Nice write up Victoria Lo
Though I also think that vanilla CSS will still be mostly used part
Frameworks exist for quick and fast solutions though for CSS, these add up to the final bundle and many optimization compromises if you add whole framework to your project.
Customization of Lib/Framework is really necessary.
Personally I as I am doing Frontend in React, and we are using SCSS on top of Bootstrap, I still don't feel like using Bootstrap as I know that I can achieve the same with much smaller vanilla CSS
And my preferences have started to shift towards CSS-in-JS
I had many interesting conversations related to the use of Tailwind and I agree with them completely. It's a utility framework and should be used when one doesn't want to touch vanilla CSS
With Bootstrap, one will always have to add some customizations with CSS