Maybe there were some entertainment related things (nightclubs, call girls, film extortion?) going on in either Cuba or Beverly Hills that would have required Fredo's attention and allowed him a plausible reason to be in those places.
Michael should have never allowed Fredo to go to Havana unsupervised whether it was for fun or to do any family business no matter how insignificant.
Yes but hindsight is 20/20. I don't think even Michael (who is smarter than anyone else) could have extrapolated that Fredo's incompetence and/or laziness/fear in dealing with Moe Green and the cocktail waitresses would mean that Fredo is a future liability and should be watched constantly.
We don't really know what Fredo's role or responsibilities are. He's listed as Underboss on the chart but that's sort of a joke, don't you think? He has men reporting to him but according to Fredo's rant he doesn't have any meaningful responsibilities, something I think Michael would agree with.
I think Michael did what he could in granting Fredo jobs or roles he thought his brother could handle. It was likely while doing one of those supposedly pedestrian jobs that Fredo complained to the wrong people and Roth/Ola were made aware of his discontent.
That raises the question of why Michael wasn't aware. I think , as I mentioned before that Michael's pride blinded him to Fredo's resentments. Also more pragmatically, assuming that anyone else knew, which person among the Western regimes would want to stick his neck out and inform Michael of Fredo's discontent or meetings with Ola?
Such a person would be taking a big risk. Michael didn't take bad news well. Maybe like Vito Genovese, Michael would have dealt with Fredo and then gotten rid of whoever told on Fredo, because well that person was a "rat"...
