I agree and have wondered the same thing. I think it's terrible timing to have Splash and HM down at the same time.
I have to imagine the thought process was to work on HM before the crowds arrive for the new Tiana's ride. I think they would rather get the HM queue fixed up to make more walking space to get to the new ride. There is ADA work, but they're also improving the queue area so it doesn't overflow through NOS and into the walkways as much, and they're adding a proper gift shop at the exit instead of the outside shop, which also backs up to the old entrance to Splash.