If you are doing business why would you not have all the proper licenses to operate.....
Because most people aren't selling coins through a registered business.
If you have some stuff you want to sell, like old coins or stamps that your grandfather had collected, worth a lot of money. Do you set up a business and register yourself as a coin/stamp trader. Most people don't. They just get adds online to FB, craigslist or whatever and await someone to show up with the money.
Exactly. But even if you DID register as a business, maybe you thought that bitcoin was not money (based on a previous court case), and so you still ran afoul of some money laundering law.