Is this a joke? I don't understand. With Bitcoin, I can see the concern due to its history, but why would it matter if your Monero comes from a miner? Also, as I understand it, only large companies, exchanges, and governments are interested in acquiring "clean" Bitcoin.
Some countries want thorough explanations on source of funds. If you can get the view key of the transaction and claim it was a mining reward, it is the easiest way to get past AML scrutiny. It just depends on what countries you live and bank in.
Sometimes you want to buy a house with crypto.
If Monero has perfect privacy, why is Monero working on enhancing it's privacy?
No matter the current state there is always the chance that every transaction on the blockchain could become exposed.
Financially, it is better for the MCEP for miners to not sell to exchanges.