Capital can move away from taxation much faster than labor, so capital has to be taxed at the maximum possible rate that does not encourage too much of it to move away from the taxing authority in question.
But capital can move away from taxation much more quickly than labour because the political institutions that capital controls _have made it that way_.
As an example: we got a "North American Free Trade Agreement" which allowed mostly free movement of capital between borders, but at no time was it even considered that labour would be able to freely move. Even for people like myself who are skilled in software, etc. it is quite difficult.
All of this is to reiterate what another poster said above: the people who control large amounts of capital have an outsized influence on the way tax _and trade_ laws are written.
