His official reason was that a tournament would be more commercially valuable if it had both Alekhine and Capa, but I don't think many accept this as legitimate. Of course, if Capa were in the same tournament with him, Alekhine would have to work much harder to come in first and also avoid a loss in his individual game with Capa. In other words, it was poor sportsmanship.

The mark of a true champion is to run away from a challenge.

Alekhine refused to play in tournaments with Capablanca. He, in effect, banned Capablanca. Capablanca never did this to Alekhine.

As I said above, he asked for a higher appearance fee, which I agree was unsporting.

That's mentioned in Whyld and Hooper's book: The Oxford Companion to Chess, although people here have disputed that info.

The Argentines would have been behind Capa in the Buenos Aires title match. They may well have worked with him and Alekhine to organize and raise the funds for the match, but as far as offering that as real solid evidence of their jointly working together, I would not go that far.

I've never heard of Capa banning opponents from his tournaments, but even if he did, it wouldn't make it right.

Getting back on topic, if the standard for a pre-FIDE champion is that he should take on all the best challengers for whatever stakes can be easily raised at the time, I think only Steinitz would measure up. Of course, he died in poverty.

I think it's pretty clear that the match fell through for financial reasons.

As for <reciprocating>, if Alekhine actually had the ability to raise thousands for a chess match with the snap of his fingers, there's a good chance this match and several others would have happened.