It would suck not being able to play the one game/franchise you really want to, and playing a bunch of fillers that are nothing more than bad wannabe clones, or worse yet something you are not even interested in.
Variety might work for some people that don't get tied down to the major titles, but for the majority the top franchises are there because there is a lot of replayability. Most of the fun is emergent and comes from you and your friends rather than whatever the game devs decide to do. A lot of the best franchises are easy to access, hard to master which adds to replayability.
Especially for older gamers who don't have a lot of free time, it's more important to be choosy and not waste your time on things you don't want to do. I wouldn't be surprised to see most of today's gamers playing 1 or 2 games overall, usually FPS, MMO, or split between the two. The games nowadays just demand so much time to grind or to keep up your skills with your peers that there isn't a whole lot of room to do anything else.
