Probably just a function of environmental input and enough generations optimizing along directions that matter more for species propagation than a large, energy burning cognitive organ. Keep in mind, it appears that Human level intelligence seems to have (so far) only evolved maybe a handful of time maximum in planetary history...and AFAWK only along a fairly specific mammalian family line that happened to live on part of the planet with fairly specific thermal/environmental and energy availability properties.
On a planet slightly warmer than the Earth, the dominant species might be selected to have heat management organs we're not even aware of; or a planet with more landmass vs. ocean, the ability to handle dry climates; or a planet with two moons and higher gravity an efficient metabolism and ambulatory system...some kind of reptilian slug perhaps?
Are savannas necessary to culture space faringness? Or could a planet with no moons, shotgunned with equally dispersed Guam sized islands provide the necessary conditions?
It's useless, but an incredibly fun thought experiment.