It probably had to do more with the evolution of chipset manufacturing and transistor counts (and costs).

The ps1 was released 1.5 years before the N64, the 3dfx voodoo chip is as capable as the n64 (maybe more so considering memory available), but I guess both Nintendo and Sony did opt for a bit more cost-efficient designs to make a profit on their consoles.

Looking at the release dates, the progression of capability is quite matched.

1994 dec 3 ps1 1995 nov 6 3dfx voodoo 1996 jun 23 n64 1998 nov 27 dc 2000 mar 4 ps2