It seems like to me that they're just phasing out amiibo in general. If you notice the general trend, amiibo support for games have dried up, there are far less announcements for amiibo, and brick and mortar stores don't even have amiibo sections any more. I think that's kind of a shame, as I've always liked the little figures for the nerd appeal and always look great on the desk, but toys-to-life is so out now.
I don't see how a paucity of majority of courses being designed for single player would be reason to completely throw out online multiplayer options, and there's that unsupported premise that multiplayer doesn't matter/is "irrelevant" because most levels are single player. Why have multiplayer in the first place!? Mind you, there is *still* online multiplayer, it's just that you can't play with your friends, and playing with your friends was a major selling point of the game, given the promotions of people having fun together, the Switch being a family console, and the cute art of characters building shit together. Doing that sort of shit, self-sabotaging your own features for ridiculous reasons (and I can't think of any other reasons beyond laziness) absolutely defeats the purpose of a new feature of this game.
But hey guys, LOCAL PLAY is supported so that's cool, and that's great! But that's not worth commending over as it shouldn't be a feature people have to worry about.