Because if KTM does hop back on board they have a contractual obligation to Michelin. And should McWilliams end up piloting the bike he will be happy on Michelins as he has stated he can ride anything with French rubber.
Although KTM wasted their money getting a deal with Michelin to use them on ...... KR bikes.
It's like buying the most expensive tires on the shop to put them on a cheap, Korean, 2nd hand scooter.