Alpha was the reason DEC was for sale. It was a very cool speedy architecture, but it took too long to emerge from the DEC management swamp.
Bitsavers has a series of memos showing how the Alpha predecessor Prism went down in flames when DEC decided to quick-fix its technology hole with MIPS.
Alpha was a kind of illicit skunk works leftover from that failed project. If DEC had pushed it out the door a couple of years earlier - not likely, but possible with a push - it might have eaten the rest of the industry.
I suspect that whatever the virtues of the Alpha architecture [1], DEC simply didn't have the muscle to stay in the game with exponentially increasing R&D costs.
[1] And it's not like Alpha was some shining beauty of ISA design either. Early versions lacking sub-word load/store, the absolutely crazy memory consistency model, ...
