GitHub ToS say (point B.3): “One person or legal entity may maintain no more than one free Account (if you choose to control a machine account as well, that’s fine, but it can only be used for running a machine).”
And “A machine account is used exclusively for performing automated tasks”.
Now, in practice, I know GitHub do not check (and people do not read the ToS). But if people agreed to the ToS, they also agreed to not create a free account. However, I do not know how it work for paid accounts.