If a maintainer has chosen to open source and use a permissive license (key word chosen, this isn't a default), they are explicitly saying via their license that they are not charging for the use of the code. What's the issue here?

If a maintainer wants to make money directly from their code, they are free to charge for it, or for services around it (examples: Sidekiq, Oban, Tailwind, not to mention large examples like RedHat or Ubuntu).

Everyone involved is making informed choices.