One can't be held responsible for unethical things done by his creation once it's sold.
In a free market everybody can choose to sell or not, who to sell to and under which terms. Therefore, he should be held morally responsible for giving away control of his creation to the wrong people, or for not ensuring his creation can't be turned into something bad.
Then again, they don't get rich by cheating, abusing or whatever, they build a legal thing and sell it. You wouldn't go after a knife maker if someone used his knife to stab someone.
If you make a successful crowdsourced reviews website by building trust over time with contributors and users, and by any mechanism it ends up getting owned by an advertisement company that makes a business out of making it pay-to-win, should you not be held responsible?
I'm not talking about legal responsibility here, just moral responsibility. Ideally the former should follow the latter but it's not always the case.
Even then, has say Databricks or Canva been guilty of unethical conduct?