POWER was not originally open for use by others, under any license terms. It also was on the trailing edge of performance for many years. The original POWER 1 and POWER 2 boardsets were enormous power-sucking bastards with price tags to match. (Yes, boardsets. They were not even microprocessors.)
SPARC and MIPS were relatively open from day one but there were fewer takers than you would expect
SPARC had a number of licensees, but most of them chose to either re-use Sun software (Fujitsu, Solborne) or sell their chips directly through Sun (Ross, Weitek)
MIPS had many licensees but it ended up being bought by one of its most successful customers, SGI. Turns out, controlling the product direction is pretty important!
The point is, there were a lot of market forces piling up to drive people to play their own game, even it looks very silly 30 years on.
SPARC and MIPS were relatively open from day one but there were fewer takers than you would expect
SPARC had a number of licensees, but most of them chose to either re-use Sun software (Fujitsu, Solborne) or sell their chips directly through Sun (Ross, Weitek)
MIPS had many licensees but it ended up being bought by one of its most successful customers, SGI. Turns out, controlling the product direction is pretty important!
The point is, there were a lot of market forces piling up to drive people to play their own game, even it looks very silly 30 years on.