In fact that's more than Bootstrap shows you. If you discount the big download button in the home page, you have to guess it's in 'Base CSS' (not Components) and navigate a few miles down.
Anyway, all this rationalization on why everyone uses bootstrap is also funny. Who could imagine a CSS framework would get people so defensive?
Look at the home page as a casual browser would. The first page has tons of screenshots... of grids. Click on "Features"... more grids. Click on "Add Ons"... more grids. Click on "Docs"... no screenshots! If I'm just casually glancing around, I feel like hitting every 1st level page is fair. All I saw was grids. Why would anybody be confused that a visitor might think this is a CSS layout/grid framework?
Perhaps bootstrap cheats by putting their components onto one long scrolling page, but it does get 1st level nav and I see what it's about pretty quickly.
I looked at all the first level pages and saw lots and lots of previews of grids, but nothing else. I only saw the other component because of your link here. Having to click in three levels before you see a screenshot if a button is perhaps misleading people into thinking there isn't as much there.