Perhaps one may suggest the following. Simply speaking, chesron mammon is an actual loss of money, as opposed to losing out on potential gain, as the gemaras in Moed Katan (2b, 3a, see there) seem to imply.
The Torah only forbade work that has a halachic name of "melacha" (the 39 of shabos etc.) with the exclusion of techumim, crossing the line of permitted travelling distance.
Therefore, automatically, everything else is permitted. The sages felt that it was degrading to the holiday to perform anything that involves excessive bother (Moed Katan 2a, see there).
However, the rabbis said that where there is a loss of money, anything that isn't too strenuous may be performed, for those instances don't express total degradation of the holiday: rather, it is understood that the action is due to the loss of money.
In a similar vein, the Ksav Sofer permits smoking on a holiday, but only on the second day of the holiday, for on the first day it would be degrading to the holiday, but the second day, after not haven smoked the previous day, the buildup of discomfort would be tremendous and smoking is no longer a display of degradation.