React is a special beast, I don't like it, yes, it's a little bloated and no, I don't so much think it's quite suited to the front/back of frontend division.
Your problem with bloat and fragmentation though, is not about this particular form of division of labour.
Front ends change a lot more for a variety of reasons.
One reason the front end evolves more is there's more going on, and more detail. The backend is logic, which can be more succinctly articulated by code. That's what code is for.
Most code was never designed for UI, and even HTML/CSS was never designed to do what it's doing. A simple web form can involve a lot of cross-cutting artifacts and complex statefulness.
Even with a great set of tools it can be quite hard to get right, and requires a different way of thinking than on the backend.
Front end problems are usually however, narrow in scope - a screen can usually only ever be so complicated, whereas on the backend, true scale can make a lot of things hard.