I don’t agree with your argument about Djokovic being from a less snobbish respected country, but I do think you’re onto something about his socio economic status.

Its definitely true that many tennis players (and fans) are firmly upper or middle class. Djokovic has had to scrap against the odds all his life much more than his peers, and that fight and determined spirit runs through his game. Maybe that’s what some fans don’t like?