This is tangential, but I believe vanity has been increasing with every generation for a while now. Each generation is more vain then the generation that came before it.

I don't know if that statement holds beyond the last 100 years, but certainly it does till then. I would chalk it up to being the result of the communications expansion, with each year our audience increases (by virtue of our increasing ability to travel the world, and by the ever expanding internet), and with that expanding audience comes a desire for us to be liked by the greatest number of them, which involves out-competing everyone else.