Filters are a quicker and more dynamic way for the nodes, including miners, to stop unwanted data. it's a tool of the whole network. If a fewminers disregard and decide that they will just mine those txs, then 1-the spammers incur in a cost, they loose the censorship resistance of the p2p network, it centralized service and pay a premium to the miners. 2-if this is considered harmful by a majority of the network, and miners are not following the gentlemans agreement, then the only choice is to force them by consensus, it's not by making their choices more widespread.

Bitcoin Knots is stopping spam to enter my mempool. I don't relay spam. Many people use Bitcoin as money. And their number will grow.