I have been using Bootstrap for this entire year on various projects at work. Nobody complained because I was using Bootstrap. In fact, I actually got a lot of compliments about how well the projects looked. The fact is, outside Hacker News, nobody cares if you're using Bootstrap. They care if your project doesn't look horrible, and more importantly, they care if your project works.

Now sure, I could learn CSS and do all the stuff you put in the last four sentences. But designing a good-looking style with all the components I needed - grids, buttons, navbars, modal dialogs - would take far longer than unzipping Bootstrap, dropping it in my assets folder, and actually writing the bloody code. Especially since I walked out of the office Friday after emailing my supervisor a two-and-a-half page list of stuff I wanted to get done this year but couldn't.