Maybe... but it achieved that default status in the first place through a lot of technical merit. It stayed there because it's largely good enough and remains with a lot of inertia, as well as the shear size of the larger community. Just MUI, Mantine and even Bootstrap component libraries are in and of themselves very polished and generally better than any competing technologies.

If there was an MUI for Yew/Leptos/Dioxus I'd probably have switched to them and dealt with the minor performance hit with wasm. And yeah, there's component libraries, but not nearly as complete or polished in usage.