Mainly becuase i have several 1Tb 2.5" hard drives already just lying around the place doing nothing... that and 1tb SD cards are £150... which i dont have going spare at the moment
If you're meaning to store that many games, you've indeed got a point, but despite being a multi-system machine, I certainly can't see myself needing more than 128 GB
The dock does have an M.2 slot, but I suppose you got it for the disc drive