More on topic, web frameworks solve the following problems for me, which I guess are things now taken for granted:
1. Provide a standard API across all popular browswes by papering over subtle differences in JS- or rendering-engines. This is kess of an issue now worh the homogenization of browser engines
2. Provide components with out-of-the-box accessibility. For me, this alone is worth the price of admissions. YMMV if yiu don't care about your (potential) users who use assistive tech like screen-readers
3. Design systems, CSS frameworks and iconsets makw my webapps look much better than if I were to be left to my own devices. I'm no designer, but the added complexity is worth it to me (think internal tools, not public products with a design budget).
4. Job mobility and the ability to transfer knowledge from one employer to the next. When I put down "react" on my resume, the reader will know exactly what I mean (as opposed to "CorpWebVu revision 5". I am also able to get up to speed on a React codebase because I know the conventions. This also is worth the price of admission by itself.