Gubber-mint said so!
After a the mower deck is shut off,
it has so many seconds to stop rotating, so when a dummy puts any part of his body in it to see if it is turning, is not posa mangle it.
That's why we have those stupid levers on hand mowers that have to be held down while mowing.

Sorta like those signs on motor home cruise control switches.
Warning:
this is not an auto pilot, do not leave the drivers seat to make dinner/potty break while engaged.