This comes just after Styles defeated Shinsuke Nakamura to advance to the semifinals of the Intercontinental championship tournament. If he were to win said tournament, it would make no sense to go back to Monday Night Raw with it, considering the red brand has the United States title.
Not that this is a spoiler or anything.
This helps fill the gaping hole left by Roman Reigns at the top of the card. There’s no telling when he’ll be back, so Styles should help the blue brand with star power right away.