Not to sound like I'm boasting, but most of my commits are far too atomic to warrant more than a first line. If I need to write several paragraphs about the changes I'm making, it's definitely too large a commit.
No one is saying to write a lot. The point is to write enough. You should basically be able to hand someone the commit log and they should be able to easily figure out how the current state of the code came into being without having to dig into the code.
Small commits are fine and often don't warrant several lines. I've done that too.
It's often a fine line between a commit that's too big and too small. At the same time, just because a commit warrants a few sentences about it that doesn't necessarily mean it was too large. I don't want to keep being long winded here so I won't go into examples as I think we've all seen situations like what I'm talking about but I'd be happy to add an example later if necessary.