If you don't want to test the coins, then simply don't mine them. If you mine them for the sole purpose of selling them, then that just goes against the functionality of testnet which depends on tBTC having no monetary value. If you finished your tests and mined tBTC, then just give them to a faucet or to someone who needs them.
It cost 5x more to mine them than it does to sell them. I don't think it's going to increase mining.
The people selling them appear to have been sitting on them for *years*.
It's healthy they go into circulation cheaper than it would be for some India kid to mine them and make the next billion dollar project happen.
*shrugs*
It's just an option.