This is just like thinking about... quitting smoking, except quitting smoking could prove a lot easier.
Many will say it's not true, and i'm not here to judge, but i think we're all kind of "addicted", and for some, it's even worse... when it stops being about the money.
Sure, fame and all that matters too, but it's the money we're mostly after, because money will inevitably bring us the fame.
A player who's on a loosing streak will always think about quitting, just so he can cut his losses, but in the end, the thought he could recover... is stronger and will make him try again.
...one who's winning, will also think about quitting, but then again... to what end, especially if he's making a living out of it.
We may quit for a while, but at some point, we come back. In the end, it boils down to controlling it.