The point is that "amateur" means literally "lover" in latin. While "professional" means "for money" today, in latin it meant "to profess a vow to do it with high standards".
For example, you can be a professional, but do things "pro bono" (for free or for public good) or "pro lucro" (for money).
For example, you can be a professional, but do things "pro bono" (for free or for public good) or "pro lucro" (for money).