And loading times. I think people already forgot how long you had to wait on loading screens or how many faked loading (moving through a brush while the next area loads) there was on PS4
Small RAM space with the hard CPU/GPU split (so no reallocation) feeding off a slow HDD which is being fed by an even slower Bluray disc, you are sitting around for a while.
So there literally were no "loading" times for these assets. This might not even be realistically possible with NAND flash based SSDs, e.g. because of considerations like latency.
Though directly accessing ROM memory would also prevent things like texture block compression I believe.