[Symmetry]

It wouldn't really be surprising. Prokaryotic life appeared on Earth very quickly after the Earth cooled down. But it took a very long time after that for Eukaryotic cells to develop. Just going from Earth history I'd expect lots of planets with bacterial mats but very few with complex or multi-cellular life.

[reubenswartz]

It seems like it happened "very quickly" compared to the evolution of eukaryotic cells and multicellular life, but it still took hundreds of millions of years, and it probably happened once or a handful of times, not all over the planet.

I share your expectations, but it's hard to know if it's common even for bacterial-level life to arise.