That then raises the question- Why wouldn't everybody do it then? Like you say, it's not complex. It would seem to me with something like GTA, the amount of data you'd need to preload in some of the cities as you're moving through them would be relatively large, so that's why the HDD might fall behind? In GTA5 there seems to me to be a ton of unique items being loaded in for the terrain. Objects they reuse of course, but for the scenery there seems to be a ton of different tiles.
Or it could just be inefficient code I suppose. PUBG's an excellent example of slapping something together on an engine that's not particularly well designed for it, in my estimation.
Wiley.