What would prevent those people to continue doing so? Those who attach great importance to their ELO and want it to represent their actual skill level on all maps, can keep all maps open and keep on playing all maps. I don’t see how allowing other people who don’t really care that much about their ELO, to play only one map, will change their own quest for a great all-maps ELO.
Well, that would be another issue.
But to be frank, it’s mostly the top high elo players who actually mind their actual ladder rank. For most people, we only mind the ELO, not the actual rank. And even for top players, they value their gaming experience over the actual ladder rank, most likely. They value tournament achievements over ladder ranking. Ladder is to practice and enjoy the game, not to have a rank or a number flattering your ego (for most people).