The
Wikipedia page about the CASA 2.111 neatly sums up the story. They had been flying He.111s since 1937, negotiated a contract to build 200 of them in Spain but had to use a cache of Jumo 211 engines from France and when these ran out of steam, needed another powerplant to replace them with. At that point, the Merlin was easily available. The
Hispano Buchon story is very similar. Both of these re-engining projects took place in the mid-50s. At that time finding German engines for them would have been very difficult if not impossible.