Lobbyists exist because of freedom of assembly and freedom of speech laws. The strongest lobby in the USA without question is the AARP because their voter list is the most likely group of voters and they are nowhere near the largest donors. Anyone talking about lobbying in the context of capitalism is unfamiliar with either concept in any level.
For pete’s sake most capitalist nations do not have lobbying.
Capitalism is not a political system. You can have monarchal capitalist systems, fascist capitalist systems, oligarchic authoritarian capitalist systems, heck plutocratic democratic republics like the USA can be capitalist. Socialism is both political and economic but not all ideologies are both.