Like I said in the "real is first team to win back to back CL" thread, it is very hard to compete against those two Spanish teams because they have a lot of factors in their favour. From location, lifestyle and weather to sharing language and cultural aspects with countries that often produce the majority of top players. They also compete in a two horse league that has a crazy disparity in revenue distribution, which in recent times has resulted in both of those clubs very rarely through barren spells trophy wise, as well as being loaded. This affects perception in a positive way for them. Then there's the fact that historically they have had some of the greatest players ever and currently have what's generally accepted as the two best players in the world being supported by all star casts.
There are clubs in Europe that tick some of those factors but they likely don't tick them all like Real or Barca. Like for example the Italian clubs have lifestyle, location and weather going for them, but they probably don't have the same money and exposure.
English clubs have exposure and money, and the ones located in London have that going for them as well, but they compete in a league that has like 6 legitimate title contenders so there are more chances of spells without trophies. There's also the different culture and language to take in consideration for some overseas players as well as cold/rainy weather. And with so many power clubs in one league it means no one club has a monopoly when it comes to the best domestic talent, United used to have an edge regarding this but it's been long gone.
Bayern has a monopoly over the bundesliga both monetarily and competitive and it's no surprise they are competitive in Europe and manage to attract majority of domestic top talent and some from overseas but they compete in a league most people don't care about.
So yeah, majority of clubs in Europe don't tick the boxes Real and Barca do or at least not as many, and this results into pretty much every player on the planet wanting to play for them, they get those players and win trophies, which boosts their prestige even further and makes them the de facto clubs to play for. It is a very hard cycle to compete against let alone break.
Edit - credit has to also be given to their academies.