The Mavic is flown all over the world, the FAA is only in the US. 400' is _not_ a regulation in the US, it's a recommendation. It's 400' above ground, not take off. So you could climb up a mountain and easily be 400' above the take off point but still not 400' above the ground under the Mavic. The list goes on and on.
Lastly, as mentioned, DJI is not law enforcement. They are not required to put a 400' limit in their firmware at this time and they are in the market to sell consumers what they want.