Er, PPC is the biggest slice of embedded market by a lot, followed by ARM. MIPS barely registers. PPC is the go-to chip for Defense contractors as well as most beefier embedded things like network routers. "Embedded" != "Low-power".

The problem is the original question presumes a couple of things (1) that Linux was not "usable" in the 90s. Well, it was and in fact I recall having been involved in several MIPS Linux development products during that decade. I also did some Linux projects on PPC. Never used the Alpha. (2) the OP is concentrating on full, general purpose systems, not embedded systems.

Not sure how accurate this information is, but I googled for Linux and DEC Alpha and found not just a promoter for the Alpha, but also for MIPS and PPC chips too:This is from http://linuxdatabases.info/info/linux.html

I do have a partial memory of hearing that DEC announced this information. So I either dreamed it or lived it.

Yes, because the MIPs and PowerPC based computers I read about during the early 90's were sold AS general purpose systems and workstations. I remember all the hype over RISC and how x86 was running out of steam.

I didn't say they can't be embedded. But there were full systems that used them