In the films, we see mostly typical human sized sentient aliens (Rodians, Gungans, Gamorreans, etc) at around 2 meters tall and a minority but still sizeable number of sentient aliens that are more in the range of human little people (Ewoks, Jawas, Ugnaughts, etc) at 1 meters tall. There aren't many in between (maybe Maz Kanata at 1.5 meters), and there aren't many smaller (Yoda is slightly below the 1m at 0.66m, Salacious B. Crumb at 0.7m) or larger (Chewbacca is just 2.28m, Kaminoans are a bit taller). There are some major deviations like Jabba the Hutt, and even some giants outside the films. But most of the aliens we see are in one of two ranges, either ~2m or ~1m.
Out of universe this is obviously because of the actors we have to work with here on Earth. Although it is interesting that Yoda and Salacious are still not far outside that 1m range even though they are puppets rather than people in suits, and so could have been even smaller. I suppose it comes down to making relatable characters...
But in-universe is there any explanation of these two size bands being most prevalent in the galaxy?