Microsoft has been willing for a long time, because they have the Xbox and PC market, where as Sony just compete with the PS.

Every step of the way Sony has tried to kill xplay and that was the difference that Epic made. When their focus groups started saying that "no Fortnite"/can't play with my friends was a reason kids were choosing Switches and Xbox over a Playstation, that equation changed. In their eyes they were no longer just protecting their walled garden, they were now losing market share over it.