It is not about TUS storage and 3GB. I have the space and bandwidth for such file. I just don't see the need.
TUS doesn't save mappacks as external files on the server. When you download a mappack from TUS, it creates the zip file on the fly and sends it you. It is designed like this to have better analysis on the maps. For example, when you download a mappack, all the maps inside gets +1 on their download count. You can edit the mappack online etc etc ...
TUS runs on 2 servers. The main is VPS which this website is running on. The second one is TUS storage which has over 500GB space. I can put the 3GB file on TUS storage server and there will be no pressure on TUS main server. But as I said, I don't see anything good about this kind of external files.