They used industry data to make the decision first to avoid potential multi minute load times for 10% or do of their players, hard to test all kinds of pc configurations. Now they have telemetry showing that it doesn't matter because another parallel task takes about as much time anyway.
Maybe it's changed a lot statistically in the last few years but for long time PC gamers used to have the mantra of small SSD for the OS and large HDD for games if they're price conscious so I could see that being assumed to be much more normal during development.
So in the worst case when everything is loaded at once (how on a system with < 32Gb RAM?) it takes 4 minutes.
Considering GTA whatever version could sit for 15 minutes at the loading screen because nobody bothered to check why - the industry could really say not to bother.
