The vast majority of games on the site is below 1 GB. Keeping your game below 1 GB can be hard at times, which is why butler allows you a size limit of 2 GB. If this still isn't enough you can ask support to increase your limit to 4 GB. 4 GB is a lot for an indie game.
The site is very generous to offer this much space without asking for anything in return.
The only people who appear to have an issue with the 4 GB size limit are making yet another Ren'Py prerendered 3D debauchery visual novel, taking no responsibility for the resulting file size and relying on others to solve that problem for them, most commonly megaupload.
So in a way, the upload limit is what keeps itch.io from becoming a den of degeneracy.