Why do we play chess?

As any chess organiser can attest, it is always better to have more players in your event than less. Well in most circumstances. And when events fall short of their predicted, or required, numbers, an obvious question is "Where did all the players go?"
However, before this question is answered (in another, later post), I think a better question needs to be asked first. "Where do all the players come from?"
This can be boiled down into a question of why we start playing chess, and why we keep playing chess. Over the years I have often wondered about these questions and I've got as far as answering the question as it relates to me. That is, I understand why I play chess, but I'm still not sure why everybody else does.
Over the last couple of weeks I have come across two interesting theories that may shed some light. The first was mentioned in Jonathon Rowson's column in New In Chess (although it wasn't is theory), and put simply, states that humans value status over happiness. In relation to chess he suggests that this may account for the value that players put on their ratings, as opposed to their enjoyment of the game.
The second theory came via the Kenilworthian chess blog. Referencing the book Made to Stick: Why Some Ideas Survive and Others Die by Chip & Dan Heath, it suggests that curiosity, in the form of a known gap in each persons knowledge, drives us. In the case of chess, we are aware that there is so much more to know, and therefore we are constantly trying to fill this void.
Putting these two ideas together possibly explains why, once you start playing chess, that you work so hard at something that the vast majority of the worlds population would find un-important.