I have found two bodies with 10, a couple with 9, more with 8, 7 is getting quite common, 6 and under everywhere I go.
A lot if it is to do with temperature, there are far fewer plant types that tolerate extremely low temperatures, the same with high temperatures. So it makes sense that most bio are on HMC or rocky because they are much more likely to be inner system bodies where the temperature is good. The other things is atmosphere, find more bio on Ammonia words for some reason, but maybe that's just because I only have a small sample.