Well, it's rather simple, but I doubt it's the sole contributor.

If you think about the constant barrage of advertisement that we're subjected to, talking about how shopping at X makes us smart shoppers, using Y beauty product will make us beautiful, and so on, the public is essentially being brainwashed into thinking they're superior to others or beginning to look down on others. That naturally leads to an engorged sense of self-importance and self-entitlement.