"You should know very well from personal observation that nearly all businesses have private lots in which the employee is expected to park..."That's not true at all.
I don't have to drive to work if I don't want to.
The parking lots are provided as a benefit to employees, but it doesn't negate the owner's terms of use, or his right to set rules regarding access.
Well,it sure is true in every job I've had;AND if one rides the bus or walks as you suggest,then there is no place for the employee to safely leave his gun unless the employer provides special lockers! To suggest the employee arrange someone else drive him to/from work is an unreasonable alternative and it is the ONLY way he could be protected whilst in transit.
What IS it about some people that can't grasp the fact that those inclined to rob,rape,and murder don't give a damn about gun laws (excepting that it makes their sprees likely to be longer and bloodier )?