when i was a fan in the 80's, hulk hogan was the most popular wrestler
he told fans to train, say their prayers, and take their vitamins
then in the 90's the bad guys became the good guys, the nwo were basically a gang that cheated to win and the fans loved it
stone cold steve austin gave the finger to authority, the rock was the epitomy of arrogance
the fans loved it
how did the bad guys become the ones people cheered?
I think there are several factors. For one, look at how music changed from the 80's to the 90's. You go from happy pop and gay-rock (hair bands) to hip hop and grunge/metal. The lyrics got darker, so did the mentality. It became cool to tell the "authority" to fuck off. The "rebel" mentality was welcomed.
However, you've got to give credit to guys like Austin and Rock. They (especially Dwayne) had lots of charisma, which shone through. It's hard not to like guys that are entertaining, whether they play heels or faces.