It's really not. Capitalism is about privately owning the means of production and extracting wealth from the effort of others. A member of the capitalist class, in other words, has passive income, because they are getting paid for work other people are doing simply because they own the entity employing them. Don't confuse capitalism with trade, which is something that absolutely exists in non-capitalist economies. And scalping too--there was plenty of scalping in communist economies, for instance.