I've always asked myself this and imo it just down to the fact that we're growing up.

Like back in the day i could spend days playing Mike Myers on MW2 with my mates or huge sessions on minecraft just having a great time. I used to love getting a new RPG game and smashing through the story then trading it in to buy a new one but now that sort of stuff just bores me

I think that a lot of us are just outgrowing videogames, or at least certain franchises.