What about "cheap to build, cheap to maintain"? I know you are thinking primarily of quality courses built by good architects, but the smallest greens are going to be found on the cow pasture rural courses.
There's one course near where I live that I don't know for sure but I'd bet was originally built with sand greens. The original 9 has some greens that would give any pictured here a run for their money. There's a wicked little 227 yard dogleg par 4 (no, that's not a typo) that has a green that's 30 feet across at its widest point (not a typo either)
I remember when I was a kid the first round that I ever played on a "real" golf course was a nine hole muni outside the Kansas town where my dad grew up, and I think it may have had one green even smaller than that (and I KNOW those used to be sand greens according to my dad) though my memory could be hazy as that was 25 years ago.
Obviously these greens will be in crappy shape because there isn't much variety in pin positions so the greens can get pretty worn especially on slopes where the balls collect, but these aren't the sort of courses that Tom Doak bothers to even set foot on and assign a 0 to