Demand does, and so does opportunity cost. It's easy enough to calculate expected returns from mining this coin vs mining another cryptonight coin (or another algo) and comparing expected BTC yield (or fiat or whatever).

Of course, you'd also need to factor in expected growth/appreciation vs other coins. Price isn't only a factor of demand, but also supply, and miners who were here from day one may (or may not) be inclined to sell at (or below or above) their opportunity cost of other coins.