It would be very difficult to list all the makers that were not allowed to resume production, but three handgun makers were - Bonifachio Evcheverria (Star), Gabilondo (Llama), and Unceta (Astra), all in the Basque region, though that area had not generally supported Franco. As Mike says, political considerations were important, but there is little doubt that quality was a major consideration, since weapons played a major role in Spain's foreign trade and Spain had had an excellent reputation for arms quality, as far back as supplying the Roman legions with the best steel swords (the gladius hispaniensis) then available anywhere in the known world.
The poor quality of the arms (especially handguns) being made in Spain after WWI threatened that trade and was very much a factor in the decision to allow only a few makers to remain in business. To some extent, it was pointless, since the Civil War had already wrecked much of Spanish industry. Of course, reducing the number of arms makers also allowed the government to keep better control of production and distribution of weapons, always a goal of a dictatorship.
Jim