jQuery emerged from a lack of standardization and features in web browsers. It was a huge step forward and some of it's core features were standardized as extensions of the DOM interface (DOM queries are an example of this)

> most often because they can't

The issue isn't skill, it's a question of common architecure. A batteries included framework gives you exactly one choice for each part of your core architecture, which accelerates development because you don't have to worry about it. In addition, it saves you time and _immense_ costs on maintaining the core architecture of your app. React is a bad example due to it's simplicity, but take Angular or Ruby on Rails. Lot's of choices made for you, so you can benefit from the ecosystem.