I think because like Trudeau the elder (and perhaps the younger) Fidel had charisma. Charisma, is like good looks - people overlook a lot of bad traits, and idolize then when they are around, and remember them fondly when they were gone...

Simple as that.. All other despotic regimes in the recent past were run by dour bureaucrats....Now Lenin, Hitler, maybe even Uncle Joe, there was some charisma...