I take it you’re thinking of virtual DOM only, which is not the problem, or the component class which hides all of the details.

React is huge, it’s unlikely you’ll implement the synthetic events, lifecycle hooks, bottom up updates, context, hooks with their magical stacks, rendering “optimizations” and all of react-specific warts.

There are simple reimplementations like hyperapp and preact and I completely recommend using those instead. I really meant React the library and ecosystem are at fault, not the general model.

never used React but my guess is, it is pretty simple to use, but most people using it don't know what happens behind the scenes

(which is not specific to React but more like an issue for any framework that tries to do everything)