For those of us who aren't super picky and don't particularly want to "grind" any specific map, the current system is preferable. I favorite Islands much of the time, but I'd rather wait two minutes and get Arabia than wait 20 minutes for an Islands match, only to play versus someone 300 Elo above or below me.
You could still select Islands along with other maps, then you don't have to wait for Islands alone. There is nothing to lose. You gain the opportunity to wait for Islands alone and reliably play it.
Microsoft has decided that those people are in the minority, or at least that the current system is the lesser of two evils as far as keeping people playing the game.
This is a fallacy. If the majority wants variety then an opt-in/max bans system would be perfect for facillitating that. Then you would not need to force variety.
*others who want control over maps. This doesn't necessarily have to do with the amount of maps selected.For others who want to play 1 map and 1 map only, no matter the queue time, than unlimited bans is preferable.
It is beneficial on other aspects as well, reduce map dodging (less time in queue and less warped elo), better elo accuracy (players aren't thrown in random maps), make MM more inclusive (no more reason to play lobby or stay on other platforms), reduce hostility in community.
Needless to say, the current system values some preferences higher than others. Maxbans/opt-in respects preferences similarly. I don't find the former ethical.