Grinding mobs for meat and sticks doesn't much make a difference which toon you are on even if it is my really crappy mage for instance.
People have been commenting from the beginning of MOP that it is extremely alt unfriendly. This is another step in that direction.
Also saying that players have sufficient notice that the Barrens "event" is ending are only thinking about the players that read forums or MMO champion the majority of the player base do not participate here nor do they have any idea that it is planned to come to an end abruptly. Blizzard has said time and again that the vocal majority is still a major minority when it comes to presence 8-10 million people playing with maybe 1/10th of that being active in the community outside the game itself. So yes it is short notice as it was not stated previously this content would just go away with the next patch.
Playstyles have also changed considerably more often I see people come and go. Players used to log in every day and be really active on my own server and in my own guild we see some players log in once and not log in again for a few weeks. It would be a poor experience to have those people on the fence about continuing to play when something they may have been working towards is simply no longer available. You cannot compare a content patch with a planned event like the opening of the dark portal or the zombie event that were events leading to a new expansion.