Well, not ALL of them need to be jerks, but we need a mix of heroes and villains to make things interesting. Muhammed Ali, referencing professional wrestling and Gorgeous George observed, "I saw 15,000 people coming to see this man get beat. And his talking did it. I said, 'This is a gooood idea!'" In the locker room afterward, the seasoned wrestler gave the future legend some invaluable advice: "A lot of people will pay to see someone shut your mouth. So keep on bragging, keep on sassing and always be outrageous."
We saw a lot of that behavior with Connors and McEnroe. Today, not so much. It's not such a bad thing if sometimes you watch a match to see someone get beat, rather than watch someone win. But, aside from Serena Williams, I don't see that so much now. OK, maybe you like Nadal, but you don't really hate Federer or Djokovic so much. There aren't really any of the "bad boys" like in the 70/80's today to cheer against. Maybe you mildly dislike Nadal or Djokovich because they claimed a fake injury and pulled out of a minor tournament to help their chances in an upcoming major, but there's been nothing like a top player getting defaulted for bad behavior (yeah, Serena comes the closest to "interesting" these days).
To make tennis "stories", we need both heroes and villains. The top tennis players should be celebrities, and if bad behavior is a reason for their celebrity, so be it.