You cannot legislate morality and/or behavior. So it's safe to say most are there to bring in revenue for the taxing authority.
Really? So why have a mortgage interest deduction, and child credit deductions? They reduce revenue. .gov is playing social engineer with the tax code.
One of the most fundamental rules of economics is this: if you make something more expensive, you get less of it, and if you make something less expensive you get more of it. By adding fees to the cost of owning drones, you'll get fewer drones. I suspect that's what they want.