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.