They could adjust the miner fees. But why? They're making more with higher fees. It's like 15BTC per block.
It's not only the miners that decide the hight of the fees, but more the people that in current situation have to outbid each other in order to make miners include that transaction in one of the first few blocks.
However, the entities that are spamming the network with nonsense transactions are heavily contributing towards mempools more and more filling up, and from there drive up the fees. It's a dirty game that is being played here.