Testnet bitcoins have no value, despite the fact that they're too expensive to mine. Since they don't have value and there is no profit from mining, what's the miner's incentive?

miner8VH6WPrsQ1Fxqb7MPgJEoFYX2RCkS right now has 1,654,132 TBTC. If we assume that they have no value, then they don't. But, since people want testnet bitcoins, why don't they have value? I don't get this. Isn't this a free market? Isn't there a demand and a supply for testnet bitcoins?