They aren't, actually, and people parrot this falsehood all the time. If we assume you're referring to the United States, don't conflate proposed rules, rules,

They aren't, actually, and people parrot this falsehood all the time. If we assume you're referring to the United States, don't conflate proposed rules, rules, guidelines, and law, nor circumstances that require you to seek FAA authorization for the flight (which is different than "forbidden by law," itself inaccurate). You are talking about Advisory Circular 91-57 (Model Aircraft Operating Standards) from June 1981. Not law, just standards for their airspace. Certainly not forbiddance by law.