Miners, for the most part, don’t mine just to support the network, but to turn a profit. As they turn a profit they in turn also support the network, but financial incentive is always going to be the primary reason for anyone that chooses to mine. There are miners out there who know that they can’t turn a profit from Bitcoin’s current exchange rate, but they choose to remain hopeful that the Bitcoins that they do mine appreciate enough in the future to compensate for their present expenditures.