And that's why two months in a hotel room won't make him easier to sign.
If you trade for MM, you trade for him as a rental, not to get a head start in signing him.
And you pay a rental price, no more.
It's different for players who grow up in an organization, from the minors to 6-8 years in the majors, they live here at least half the year, they have friends throughout the organization and ingrained loyalty - that's a strong reason for Philly teams to grown and resign their own, you know them better and you have a much better shot at retaining them.
Even if MM went to a WS with the Phillies, it wouldn't make him easier to sign - he'd see the Yankees or Dodgers as the same chance of success in 2019. He has no built in pull to this city and will make his decision the same way he'd make it if he didn't play here two months - money, location, team, family preference.