It doesn't matter that much, of course, if Valve never finishes the Half Life series; they'll no doubt continue to make other projects which rake in the bucks. But for most companies you can't just abandon a cash-cow project like that. What would happen to Toyota if all the engineers decided they really wanted to work on sports cars and nobody could be bothered to work on the next iteration of the Camry? What happens if all the employees for the water company decide to design a new dam and nobody stays on the maintenance team to stop the existing dam from bursting?