QEMM386 for DOS did not have a memory compression feature. Only one of the later versions for Windows 3.1 did.

CPUs really weren't up to the job in the pre-Pentium/PowerPC world. Back then, zip files used to take an appreciable number of seconds to decompress, and there was a market for JPEG viewers written in hand-optimised assembly.

That's why SoftRAM gained infamy - they discovered during testing that swapping was so much faster than compression that the released version simply doubled the Windows swap file size and didn't actually compress RAM at all, despite their claims (and they ended up being sued into oblivion as a result...)

Over on the Mac, RAMDoubler really did do compression but it a) ran like treacle on the 030, b) needed to do a bunch of kernel hacks, so had compatibility issues with the sort of "clever" software that actually required most RAM, and c) PowerMac users tended to have enough RAM anyway.

Disk compression programs were a bit more successful - DiskDoubler, Stacker, DoubleSpace et al. ISTR that Microsoft managed to infringe on Stacker's patents (or maybe even the copyright?) in MS DOS 6.2, and had to hastily release DOS 6.22 with a re-written version free of charge as a result. These were a bit more successful because they coincided with a general reduction in HDD latency that was going on at roughly the same time.