Baltimore has run enough businesses out of town over the last 50 years. I guess the mayor figured SOME jobs should be left in the place.
Consider the politics of such a veto. Obviously in a Democrat dominated (only) city like Baltimore the way to keep the voters happy (in the short term) is to raise the wage. Everyone would have declared how it was a victory for workers etc. And yet it seems that the good mayor was mugged by economic reality.