"Big boys" do though. And that is my point exactly - if there's enough tx volume (driven by consumer adoption first and foremost) to warrant this expense - someone will do it. Also, in reality bitcoin isn't all that decentralized. Sure, individual nodes on the p2p network are all over the place however the vast majority of them are members of mining pools, with 3 biggest Chinese pools accounting for 30+ % of the total hashrate.
So if one of the major card networks steps in and takes over that chunk, as a consumer I'd be looking at a more reliable system to deal with.