I'm one of the people who has certainly noticed unjustified contempt for Ringo over the years. I'm surprised that so many fans here haven't noticed. Many times I've heard people knocking Ringo; even Beatles' music admirers.
I think that maybe (I said, maybe!) the main reason is because when they were famous in the sixties, people were comparing Ringo's songwriting skills with John, Paul, and George. And, also perhaps, comparing Ringo's looks with John, Paul, and George in the screaming girls phase. And, perhaps, the 'drummer being a guy who hangs around with rock stars' kind of thinking.
Anyway, I don't know for sure. But, we've had this discussion in the past I think though some time ago.