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.
I think this prejudice only exists within this community where if you aren't that special snowflake you're not cool. I'd guess 99% of web traffic has no clue what Bootstrap is, what it looks like by default, how it is different when it is skinned. I would guess more than anything that they just think, this is what a website looks like now-a-days.
I'm happy to use it too with very minimal tweaking because it looks good out of the box, way more pleasant than browser defaults, it works well, fairly well maintained.
While that is true I think that most users will be oblivious to the commonalities - as developers we are not only familiar with bootstrap but also with the myriad developer-built sites that are more likely to use it
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.