Fast 7 Movie

In during the fast and the furious series there has been a heap of new characters being introduced but the one thing I don't get is why Paul Walkers crew in 2Fast2Furious wasn't introduced in any of the future fast and the furious movies for example: Ludacris plays Tej but where's his girlfriend Devon Akoi who played Suki in 2Fast2Furious and where is Eva Mendes at? and even the police officer from the first and second Fast and the furious movies Agent Bilkins