The sad part of this is that it's so easy to make your Bootstrap site look a little different, even for non-designers. I'm sure the idea here is "oh, I'm just making a quick MVP, or even a pre-MVP, or a weekend project, and Bootstrap makes the design super easy!" But if you're not going to change it at all , you might as well stick with browser defaults and not include a stylesheet at all - at this point, uncustomize…
I think the problem is that it's not very easy. And that's why you see so little variation (combined with a certain amount of laziness, of course). Editing the CSS directly is pretty much impossible for mere mortals. And of you're not familiar with LESS and compiling styles, you're going to have trouble.