Phoenix will have a high temperature of 115 degrees today. Over the next ten days, the lowest high will be 107 degrees (most days are 110 or higher). There is a reason outdoor sports do not take place in Arizona during the summer.
The pool of MLB players that would need to be isolated is 1800 players (compared to 330 for the NBA at the start, dropping to 240 in mid-August).
The amount of time MLB players would need to be isolated would be more than double the NBA players, pre-playoffs. Playoffs would be about the same.
Apparently the Marlins’ outbreak occurred after some late night outing to an Atlanta strip club (not confirmed exactly where it started though, as tracing is not exact)...that type of decision-making seems like much more of a problem than having to travel to different ballparks.