I agree, which is why I'm not advocating writing or designing your own toolkit. Instead we as a developer community should focus on the "next generation" of toolkits for the modern cross-platform world. Take all that we have learned from GTK, Qt, Flutter and all the web stuff and incorporate it into something new for the next 10-20 years.
Rust is a nice language for that since it is already a "next-generation" language in terms of memory safety and its momentum is still building. Projects like Druid, while far from ready, are a good starting point.
Style is just one of many things. And it's extremely hard to properly code your own consistent UI toolkit.
On top of that every platform has a myriad of platform-specific behaviors that people expect and that you will get wrong in yours. Accessibility is the big elephant in the room. But even things like secondary focus in prompts/dialogs on MacOS (that Apple's own Catalyst and Swift forget about) is a bitch and a half to get right.