Unfortunately, you can't compare development frameworks to UI frameworks. No one knows that you're a dog on the Internet. But anyone without technical knowledge can see a site that's built with the default Bootstrap skin and say - hey, I saw it before.
Bootstrap is good and clean framework, it is _great_ for developers. But just because it is so widespread and highly visible, there's some of prejudice around it.
Nonetheless, I'm using Bootstrap in my projects and happy with it.