why
Because it prevents others from driving up the aisles of a parking lot. Backing out is a different action, a single two-point operation without the space constraint of a parking spot, without cars on each side ...
It is quite popular in Honolulu, but results in jammed up parking lots as crappy drivers jockey back and forth, blocking the lane completely. Either do it fast, or if you cannot, do not try it at all and just pull the F in and get out of the way.
So they can write a ticket for violation of registration.
Lazy ass people being paid by tax money.