It's pretty hard for someone to make something worth a billion dollars then sell it, because someone else could make the same thing and undercut you. We even have a word for the way around this: 'moat.' In the 2000s 'network effects' were the most common moat, and they seemed a little crappy but not outrightly evil. Now the most common scheme seems to be breaking law until your big enough for the rules to not apply. That's why people see it as cheating.
Is it hard? It seems like if you have capital you just buy your moat, isn't that what basically every modern billionaire has done to get there? SpaceX used it's capital sued the U.S. government to get it's contracts and now 20 years later the regulatory capture and Elon's influence in government as a whole is beyond most people's wildest nightmares.