The 5 passenger maximum was just the most popular option from the respondents, 'with some saying that the type of aircraft, rather than passenger numbers, should be considered when setting limits'
Seeing as aircraft such as the Caravan and PAC750 are carrying over 15 people to flight levels every day around the country, often by private pilots, can't see how the 5 seat limit has a compelling 'protecting the public' case.
Operators with AOCs also use 50 year old 206s etc. I don't see the distinction. Think of it the other way: a baby boomer that sells one of their investment properties, goes out and buys a new 206, hires some young pilots and starts a business where previously there was nothing.