Makes perfect sense to me. Becoming a billionaire requires making a chain of morally repugnant decisions. Beyond a certain point (which is definitely somewhere below $1B) it takes more than just having a successful business to continue growing because there are obstacles in the form of competition, market saturation, regulations, etc. There must exist some moral line which most wealthy people - having the resources and being in a position to do so - decide not to cross, and therefore don't end up becoming an oligarch. In some cases that line might be lobbying the government to weaken or remove regulations(environmental, consumer and worker protections, etc.), or colluding with others to set prices, or exploiting tax loopholes and government subsidies. Every billionaire has done something like this to get to where they are. It is impossible to reach those heights with only conventional business practices.
That isn't to say that every wealthy business owner who isn't a billionaire is a saint. They're still engaging in exploitation to get ahead, but in most cases it is the conventional and societally accepted form of exploitation that we take for granted under capitalism. Billionaires aren't just your average business owner, they're the best at capitalist exploitation, and that takes more than just doing it by the books.