A lot of things like this would probably fall over in court but they’ve simply never been tested yet.

D.C. legalized recreational marijuana under local law by initiative, including, explicitly, gifting, but as I understand it requires a license to sell it, and the licensing system hasn't been set up. The buy something else and get gifted weed is a workaround for that, but it probably only works because the District government itself sees the problem as being its delays in getting the regulatory and licensing set up, not because it is necessarily actually compliant.