The versions you'll find that contain 50+ GB are versions that include an extensive amount of mods. What you can download from Steam is the base game, which is still fun and has a lot of content, but the modding community for HS2 (as well as other Illusion Games) is very active, constantly creating new content in the form of outfits, SFX, maps, characters, Studio Neo assets, and more.
If you're interested in a modded version of HS2 with lots of the abovementioned additions,
this post from turbojoe will be helpful to you.