At some point you really do just have enough money.

Well there is people to whom no amount of money is enough money. Not that it is at that point about, what you can do with that money. Rather by then the amount of money is a leader board and score board all to it's own. The desire to be Forbes number 1 and then to be forbes number 1 with ever increasing lead to the number 2.

However all indications are, Gabe Newell isn't one of those people. He would have had plenty of opportunities to cash out and then do some other business dealings to get ever bigger score card number. Don't really know exactly what else it would tell of him or his character, but the one thing we can pretty confidently tell is "it seems he isn't about just singularly amassing ever growing pile of wealth as large as possible". He would have had plenty opportunity to enrich himself way more aggressively and he didn't.