Simple.
A portable, self-contained low-power , squawk 7000 unit will tell anyone else equipped with radar, TCAS or whatever that there is something around that doesn't want to be hit by another aircraft, and probably doesn't want to hit them either!
No-one really cares who the pilot is, what the G-REGG of the aircraft is or anything else. Just that someone is in the air.
And if it could be the price of an iphone, all the better.
There are people flying around in aircraft that cost less than some drones!
And if you have a share in an aircraft, that often costs well below the price of any currently available transponder (and its installation).
So price is important. And safety is important. Keeping it simple makes it work.
So why not put the three together?
Ah! I forgot! This is aviation we are talking about.