They are actually trapped in their own planets, it's very likely that multicellular complex intelligent life develops the most on super-earths with higher gravity (thus a better magnetosphere), less mountains in the landscape, shallow oceans (or not) and a greater biodiversity, a K-type star would provide ideal conditions

This would mean that they would be taller than us, stronger but also more burdened due to the high-gravity, trying to escape the planet down from the surface up to the sky and space would be incredibly difficult, which means they are literally imprisoned by their own large planet