I don't get the confusion over the remastered courses quality. This is extremely obvious. They've been working on Mariokart 9 for a while now, and didn't anticipate Switch 1 to sell as well as it has. They are delaying the launch of Switch 2 now, and trying to get MK9 out as a launch title, so the amount of internal people they have to throw at their current MK game is very minimal, but they can't ignore it as it is a gold mine and will boost NSO+ subscribers a lot, so they put a small team on 8D and maybe some external people and they just do the easy work of remastering courses over a slow period.
They just want to make money while the main teams works on 9. Simple as that. There should have been no expectation that they'd remake maps, they said remastered in the trailer. It just means 9 will be out sooner so we should all be happy about that move on. If they remade these maps 9 would come out even later in Switch 2's life.