Or people who are not interested in dealing with the cross platform complexities of HTML and CSS over multiple browsers, mobile, and so on when someone else has kindly solved the problem for them. Maybe they have other things to worry about such as marketing or work on the rest of the product.
That makes sense, thank you. But for those of you who find Bootstrap a little bit overkill, do check out:
Not at all. It saves you from writing the same boilerplate code you write nearly every time you start a project. Familiarity with HTML and CSS has nothing to do with it.