A redditor said it best:
The reason is obvious. Disney is a left leaning company and would choose to add diversity into their movies for the sake of race identity politics.
That said, i dont mind but i would prefer disney to keep politics outside of entertainment
also i dont find Halle bailey attractive (not cuz shes black ofc)
Update: Halle Bailey actually sounds like the old ariel. I can hear it in her voice. I just hope that's why they picked her