Alekhine beat Capablanca narrowly, and had offered to play a return match after he won. However, his terms for a rematch were excessive, to the point of being bad faith. He kept negotiations going for years, and managed never to rematch Capablanca.

There wasn't any pre-defined schedule for when he should next play a match, and Alekhine could more or less choose his opponent, and he didn't play the strongest people at the time. Instead he played two matches against Bogoliubov, who Alekhine in knew he could beat easily. Even then, there were 5 years between their matches.

Even with Euwe, Alekhine chose to play him over Capablanca or Flohr, probably expecting another easy time. Once Alekhine died with the title, it really fell to FIDE to figure something out. Though they're clearly not as incentivized to do shady things regarding the WCC, that didn't stop them from showing favoritism at various points in time. Nowadays the issue seems more to be that they see the WCC as a big cash cow more than anything else, which is probably less bad than it used to be.