The poster I replied to indicated that the “making money” part could come later.

It is easy enough to have a volunteering agreement that catches this with clauses. Open sourcing the code won’t help with that scenario anyway.

But if it were open source, volunteers could fork and self-host the application and create their own competing non-profit/organization.

It’s a content-driven website with user submissions. They don’t even claim copyright or ownership on the content, which is the actual thing that makes up the unique value.

Open source what, exactly? You point makes literally zero sense