Cena was legitimately liked by fans from 03-06 then they started to turn on him because of staleness and his matches started becoming bland. He wasn't Vince's first choice either but circumstances changed and he got himself over. He also had a midcard run to build his credibility up with the fans.
Reigns was chosen and superman pushed from the start, and what made it way worse is they pushed him over their most over face -- D Bry. There isn't even a midcard now, compared to when Cena came up where it was filled with beloved vets who could work and get new talent over. They tried to repair Roman after the fact by having him wrestle those types of matches in the main event against guys like Bryan and AJ.