For those that don't have to customize it, it 'just works' right? Also, their only major competitor was blogger at the time which, IIRC, was far less customizable and monetizable.
It's dominant in its space and definitely belongs on this list.
As someone that has created and destroyed so many blogs, it was easy to get going, choose a theme, and post. At one point, they may have gotten $10-20 from me so I could use my own domain. Not sure how they make their other money.
That and the fact that most themes/plugins are coded by juniors, in the best case...
So, yeah, it “just works” as long as you don’t actually pretend to use it for something useful.