An ESP32 is a powerful thing, but it is also a microcontroller.
They are programmable as soon as you have physical access. They are NOT like whole PC's that you can lock up with passwords etc.
More like a gun that you can fire as soon as you have physical access.
I wonder where the expectation has come from? People seem to think that it should be different than it is.
Of course they would test against all imaginable vulnerabilities. It is a weapon after all.
And of course they would make all the needed software tests in a safe environment where the switch doesn't really destroy things.
As I said, no direct profit from the kill switch. But the possibility of indirect profit: for every destroyed weapon, you cannot sell spare parts anymore, but then there is the potential to sell a new weapon later.