I don't dislike Rupp particularly, but the reason I'm not a fan and find it hard to root for him is, for starters, he's Caspar Milquetoast. His responses in interviews so often sound like boilerplate material. He lacks much passion when speaking. He seems to give interviews because he's expected to, but doesn't come across as all that enthusiastic about it. That said, he has certainly gotten better in recent years, but he still tends to come across as kind of an Android.
His running comes off as similarly machine-like. He's like a mercenary. As someone else said, in the 2016 Trials he's drafting off of Meb so closely he repeatedly clips his heels to the point that Meb, who is a very polite guy, finally turned and complained and waved him away. I've never gotten the impression Rupp is the type of guy who would ever willingly share the pacing duties up front in a marathon in camaraderie with the other guys. He's a one-way street, perfectly willing to take but never to give.
Then, he's been basically an appendage of Salazar his entire career until he was forced out from under Salazar's mother-hen wing, but through no initiative of his own.
Not to mention Salazar's sleazy behavior for years and years. Why would anyone with any personal gumption stick by a coach like that through the numerous incidents like the completely spiteful, trumped-up, and totally unwarranted Gabe Grunewald disqualification brouhaha, or treating Mary Cain the way Salazar did, to name just a couple, plus all of Salazar's other behavior mistreating other people that has come to light over the years?
Either Rupp was wilfully ignorant of it or ridiculously naive, both of which are bad enough on their own, or none of it bothered him that much and he was looking the other way, which is just as bad. And I stand by these comments when it comes to the other athletes who were with Salazar through the range of incidents as well: Hasay, Rowbury, Centrowitz, etc. At the least, even if you were one of the golden-girl or golden-boy faves of Salazar's, you would have to be living in your own bubble not to be aware of how shabbily he was treating the others around you. It boggles my mind that the favored few in situations like that can overlook that stuff in good conscience, but they seemingly often do.
And this is without even getting into the stink of the PED issues surrounding Salazar that make you wonder about Rupp. Many reasons that can make it hard to root for Rupp while still respecting his incredible drive, determination, talent, and tough-as-nails grit, and the ability to show up on the line race after race after race, dominate, and get the job done.