Honestly, I think James Wyatt returning to D&D is mainly because I don't think he wanted to leave D&D in the first place... but he saw the tea leaves of what happened to all the designers on a new edition once the book got released.
I mean, we all remember the "Christmas releases" that happened pretty frequently prior to 5E. With the exception of Chris Perkins... anyone who had worked on the D&D team for any length of time (and thus had probably a bigger paycheck due to annual salary increases and such)... were either let go or they decided to move on before the could be let go. Monte Cook, Rodney Thompson, Greg Bilsland, Bill Slavicsek so on and so forth. Then the department would bring in newer and less expensive writers and designers to take their place.
James Wyatt had been with the D&D department from at least 3.5 (and the Eberron stuff) up through 5E's release... so knowing what usually would happen around that time for an employee like him, he got ahead of things and was able to facilitate a transfer over in Magic: The Gathering, which at least allowed him to stay employed with Wizards of the Coast. But he NEVER lost his desire to work on D&D, which is why he had been writing and releasing all those Plane Shift articles in his spare time over the years in and around his Magic work.
So perhaps with this new Wizards & Digital re-org there was a growth of salary availability within the D&D department that gave him the opportunity to now come back over at whatever pay scale he's currently at.