But the data binding part isn't the same across frameworks. In Vue you have v-model, in React it's props and so on. The way you build a custom Select Dropdown, for example, will be very different between the two.

Sure, the actual HTML/CSS parts will be identical, but the JS portion is the issue here, because frameworks simply handle things differently there. In Vue you have reactive proxies getting passed around and a custom event system, whereas in React it's all objects and methods passed around as props.