Most of the developers here are indie developers just starting out in game development, so they're limited to 1 GB (itch.io's basic plan).
I think it's possible to upgrade the basic itch.io plan, but i think that requires money, and indie developers starting out for fun or with a single project can't usually afford it.
(if you don't believe that there is a limit on file size, i recommend that you to try creating a project here and try uploading a file. You will see the text that tell you the limit of 1GB)