That's just it though: NEW story. THis is not Mass Effect 4. There is no reason anything needs to be carried over.
No it's not, the devs told us that awhile back.
"To call the next game Mass Effect 4 or ME4 is doing it a disservice and seems to cause a lot of confusion here," BioWare community manager Chris Priestly wrote on the company's forums.
"We have already said that the Commander Shepard trilogy is over and that the next game will not feature him/her. That is the only detail you have on the game. I see people saying 'well, they'll have to pick a canon ending'. No, because the game does not have to come after. Or before. Or off to the side. Or with characters you know. Or yaddayaddayadda."
However it is a Mass Effect game. Just like Bioshock Infinite is the sequel to Bioshock despite having a different setting, tone and characters. It still carries some of the themes and ideas of it's predecssor but uses them to tell a new story and explore different concepts.
Yes you are right its a legitimate decision to move on but only if the way it was concluded was satisfactory. It was not.
A conclusion was presented, extended, and an epilogue provided. The galaxy changed dramatically, the Reaper threat was ended and Shepard's tale concluded. You didn't like how it ended, that's fine, but that dosen't mean they have to go back and retell you what happened.
And I said it was "easy" because if they were intent on ignoring it then it wouldnt have made much difference if they ignored it in another galaxy or in the same one.
Actually it does, by moving to a new Galaxy they avoid presenting a Milky Way that dosen't conform to what the fanbase expects from their decisions. They allow them to believe the universe the affected is as their head canon wishes it to be, while not forcing new comers to play through the first trilogy to understand all the nuances of the tale.
Going to another galaxy does make it easier to ignore but it also essentially cuts off the previous 3 games, it doesn't matter what you did, it doesn't matter in the slightest.
This is silly, you saved the galaxy, that dosen't change because the next adventure takes place in the Helios Cluster of Andromeda.