Well, there are several reasons, of course but one of the more important is pointed out by Theodor Adorno,* who wrote:
“The concept of connections, a category of mediation and circulation, never flourished best in the sphere of circulation proper, the market, but in closed and monopolistic hierarchies.”
The patronage system is challenged by market-based activities where transactions are valued according to more transparent criteria – in other words, we should support capitalism (with a peg on our noses if necessary) as a stage in the struggle against the existing feudal order.
* Adorno, Theodor, Minima Moralia: Reflections on a Damaged Life (London and New York: Verso, 2005), translated by E.F.N. Jephcott, p.23.