2) Proven player
One of the reasons why the Mets may not consider bringing Murphy back is that they have a options at second base, like Wilmer Flores and Dilson Herrera.
Flores, who’s played shortstop for most of the season, would be more comfortable at 2nd. Herrera, who’s played sparingly at 2nd this season, has potential.
Unfortunately, neither of them would be an upgrade over Murphy. Flores is a proven player and he’s had some big moments offensively, but he is still not at the level Murphy is at, offensively. And Herrera is not yet proven, and who knows how good he will be.
Murphy is already a proven player who versatile at multiple infield positions. Along with second base, he can also play first and third.