Not all shorts are thin and light...there are shorts out there that are thick and light too.
It all depends on the company who's making your shorts. The whole thick or thin thing can be due to the materials they use. How the materials are woven together and applied together when they are stitching up the product.
I could be wrong you could prob pop off an email to the company that makes the shorts you're wearing and see what they have to say about it.
I have some Bib shorts that are light and thin that I normally wear when the weather's above 65f. Then I have some bib shorts that the material feels a bit thicker but are still light. This bib’s I tend to wear when it's below 65f.