That’s just making thing needlessly complicanted in some countries. Registering a business is something you can do rather easily, I know people who have a company registered, just in case. It makes everything easier, less troubles with taxes and better legal protection (as in: a failed project won’t cost you your home).

Indie maker is a nice label, but if they're attempting to make money, they're acting like a business and should operate with a certain degree of transparency. Self-employed or a separate legal entity is a technicality.