although facebook can continue to grow,

there are other ways that can turn out to be much more profitable, possibly they took all of the talent they had and called it a day, walking out with they're successes.

but also with so many crucial employees leaving, his desire to work there has diminished.

could be quite a few reasons, but either way, to the ones who quit, they had an amazing run with what they have made facebook to become today.

These guys have been at Facebook long enough that all of their options are vested. There's little chance they are actually selling their shares, but since they are vested they already own the equity and staying any longer has less upside. I'm sure that they have been given additional grants, but their early equity is worth so much that later grants are almost meaningless. Hence, there's little economic incentive to stay.

Couple that with a changing of the guard which makes the early employees have less power and it's normal to see. This is a typical evolutionary step for any startup company. These guys are likely interested in finding a situation where they can have a big impact again with a lot of economic upside.

Sean

My haphazard guess would be that the people who pioneered the site do not like the changing dynamics of the recent big time execs brought in, and see an open window to use their unique, and valuable knowledge, to forge some new and better ideas, in which they have more control and respect.

I know I would.