Spain is where the modern game was assembled. Cruyff arrived in Catalonia in the seventies and rewired the way Spanish clubs think about possession. La Masia turned out a generation that won everything, including a World Cup. The Spanish Football Federation built a coaching culture that produces winning managers across England, Italy and Germany. Periodización táctica, juego de posición, the rondo as a training method, all of it has a Spanish accent.
A youth or pre-season tour in Spain puts your players on grass that Iniesta and Xavi trained on. It puts them under coaches who learned the game from Spaniards who learned it from Cruyff. It puts them in stadiums where football is taken seriously by an entire country, on a Saturday night, in front of forty thousand people who care more than your home crowd ever has.
That is the difference. You cannot replicate it at a tournament in Florida or a camp in England. You have to fly the team in.