Why do people like Shelton?
Because he has pretty decent in- ring ability. I get your point, but the decent in- ring, no charisma or personality thing applies to many other while we're at it, like Jeff Hardy, John Morrison (although he's more of a spot monkey), and Charlie Haas.
However, in a world of below average wrestlers with below average personalities, like Ryback
, people naturally do like Shelton Benjamin.