Understandably there's obviously a difference, but a generator would give a more accurate visual depiction of what went on in your own personal franchise. Plus it'll self generate. Why go through the trouble of "sorting" through uploaded user generated games when the developers could simply create an ongoing "generator" that will be forever active within the game itself. No need to rely on an external source (i.e. community uploaded data).
Your proposal relies on the community to keep the highlight reels fresh. What would happen if EA decides to shut down this existing database. Online is "unstable" territory; You can't always rely on it. Hypothetically, what happens if Madden 15 is EA's best offering, becomes legendary, and subsequent releases completely tank, and the NFL pulls the plug on EA?
Ten years down the line, little Ava or little Timmy wants to fire up Madden 15 with her/his PS4/XB1 and the online database is shutdown. What happens then? With an in game generator, around the league highlights will always be relevant, and the pure offline gamer can get the full game experience if s/he never once connects online.