>72pin simm in 1988 Afaik other companies picked up 32bit simms very slowly. SUN in 1991 in SPARCstation IPX. First x86 support showing up in 1992 on 486 boards just before introduction of VLB slots. Apple was year later with LC III/520 and Centris in 1993.
Simple arithmetic shows you that you can't route a 32-bit memory bus over 30 pins. You need banks of SIMMs and that means they need to be matched.
But the 386DX was too expensive, because it needed a 32-bit memory bus. So it didn't sell well and was mainly used in PCs used as servers. PC servers didn't really exist yet in 1985.
That's why the 386SX was invented, with a 16-bit memory bus. It meant the motherboard only needed a 16-bit memory bus, meaning it was much cheaper.
But that means it doesn't really need 72-pin RAM.
It wasn't until the 486 (and 68040) went mainstream that ordinary desktop computers needed 32-bit memory buses and therefore 72-pin RAM, but over time, economies of scale drove down the cost of 72-pin RAM so it became cheaper and gradually got adopted, and the 16-bit-bus 386SX (and derivative chips with the 486 instruction set, such as the 486SL and 486SLC) gradually went away.