The whole point of idTech5 is megatexture.
This is just a total non-issue. In terms of cost disk storage is the cheapest resource in computing (second-cheapest actually, after tape, but I think we can rule out tape here...). CPU and GPU are expensive, memory is expensive, disk storage is dirt cheap.
Think back to Quake 2. A full install, including patches and videos, is almost 400mb, and that was at a time when you'd commonly only have about 2gb total. 1tb is common nowadays, so 75gb of that is proportionally much lower than Quake 2 was.
Of course this is a problem if you want to install it to an SSD, but otherwise: what are you complaining about anyway?