Answer:
The argument exposed in the question does not address the fact that natural resource scarcity and/or depletion cannot be so evident, and as result, economic agents do not necessarily have the incentive to hold more of them, and drive up the price.
Besides, natural resources provide ecosystemic and enviromental services, that generate positive externalities, and these positive externalities are not accounted for in the prices (this is why they are externality), causing the market prices that are paid for natural resources to be lower than they should.
The government can use to strategy to promote natural resource conservaiton:
1) Account for the positive externalities, and increase the price that is charged for the use. It can be a tax.
2) Simply step in and forbid the use of some natural resources after a certain point is reached. It can be a quota system.