Huh? Plenty of things needed more than 4 GB RAM in the 1990s. Scientific and database applications, to name a couple examples. That's why IBM, Sun, HP, SGI, DEC, etc. were all shipping 64-bit machines then. There were also a lot of contortions implemented to make >4 GB happen on 32-bit Intel machines too.

What AMD did (and Intel subsequently copied) with x86-64 was to significantly drop the price of 64-bit capable hardware, to the point where it shipped on personal workstations which didn't really need it then.