True enough. It never makes that much sense in the show. I think they somewhat tried to follow the idea from LOTR that each group has a certain regional accent, like the Hobbits were west country and orcs are Cockneys etc (and they didn’t keep to it that well as there’s a Scottish Hobbit for some reason).
So the Starks are from the north so generally have northern English voices but Sansa just speaks in RP. Her mother sounds Irish even though none of the rest of her house do. I don’t really care because it’s all fantasy and they aren’t trying to portray a realistic region but Aiden Gillan seems to have ended up in his own no man’s land when he really shouldn’t have bothered and just read the lines in his own voice.