They both had multiple disses toward each other. The problem was Flip was facing label trouble at the same time T.I. was ascending, on top of various high profile people backing T.I., even though he was firmly in the wrong and the root of the beef in the first place.
Flip wasn't in label trouble in 2004. Dude had one of the biggest songs out and was fissed at the height of his popularity.
High profile people siding with T.I. is beside the point as well. Same goes for how ridiculous the beef was to begin with (as most beefs are silly and only entertaining because of the songs/disses). T.I. dissed Luda and it was nearly unanimous that Luda killed T.I. Luda was considerably bigger than T.I. and had way more industry respect at that point. It didn't stop T.I.'s momentum and dude was somewhat of a liability because he was fresh out of jail.