Alpha NT didn't become popular because of price and compatibility. DEC wanted to sell Alpha in serious workstations and servers and only made some half-hearted attempts to target the consumer market. Meanwhile the consumer marker coalesced around Wintel and Intel could leverage that larger volume to reduce costs, while consumers were locked in to x86 for compatibility.
Dunno much about the history of MIPS but I imagine it was a similar story. Once Windows on x86 hit critical mass it steamrolled the rest. PowerPC was the exception with Apple, but even they didn't really start biting into bigger market shares until they switched. The dominance wasn't technically motivated (I know at least Alpha and SPARC had superior performance in many areas), it was economics and compatibility (and some shady dealings).
All the RISC architectures had superior performance over x86-32 in the '90s.
MIPS is much larger than SGI, and POWER [1] is much larger than PPC (or Apple). MIPS and POWER have been used in consoles, for example. That is volume! Especially MIPS, is used in embedded chips (together with predominantly ARM). Those are found on every mainboard, laptop, console even though the latest gen consoles run on AMD64.
Alpha however, died somewhere within DEC/Compaq/HP.
My friend argued the NSA was using Alpha processors internally, and had their own fab. I have no clue about that though.
Dunno much about the history of MIPS but I imagine it was a similar story. Once Windows on x86 hit critical mass it steamrolled the rest. PowerPC was the exception with Apple, but even they didn't really start biting into bigger market shares until they switched. The dominance wasn't technically motivated (I know at least Alpha and SPARC had superior performance in many areas), it was economics and compatibility (and some shady dealings).