This guy in this video I'm posting was affiliated with both Jay and Cam and/or their affiliates and pretty much explains the whole beef between the two:
What I got from this is that Jay never really vibed Cam, while Cam made every attempt to befriend Jay, in a sort of obsessed manner.
Jay and Cam knew of each other from their hustling days and when Jay bumped into Cam the studio unintentionally he basically curved Cam who wanted to get Jay to appear on one of his songs.
This animosity carried itself over to Puffy's No Way Out tour of '97. Mase and Jay had there beef brewing, and since Mase (and Cam'ron) where "blooded up" and Jay had affiliations with the Southside Crips, who were on tour with Puff as his security, being that he was cool with B.I.G. and his boy D-Roc, there was tension which resulted in Jay leaving the tour early.
Mase addresses this in a dis to Jay-Z:
"All summer long you been ducking piru...
And half y'all nikkas was scared to buy blue"
And of course we all know about Jay stabbing Un, who was basically the Suge Knight of the East Coast and a Brooklyn legend, who Cam was also signed under and basically "extorting" or "robbing" Cam ou of his money.
I think Jay's disapproval of Cam is because although he sort of hustled it was cousin Freeky Zeekey who was really knee-deep, while Cam fabricated his lifestyle.
This is evident by the fact that we repeatedly over there years have heard about Cam'ron being punked, whether it being him having the saliva slapped out of his mouth by Tru Life in public, or him being chased out of his own neighborhood basketball park by Junior Mafia and jumping over fences in Timbs like Equestrian, or him getting assaulted in a Harlem park in 1999 and filing a police report even though he went on national television years later claiming that he's never snitched.
All of these factors contribute to Jay's discontent towards Cam and Dipset, and it's not just some weird obsession as others are trying to present it as.