Simple. Do you like sleeping in a clean bed or a filthy bed?
Just kidding (mostly). I think this really breaks down along blue/white collar lines. If you spend your work day turning wrenches, doing physical labor, etc, you’re going to want to shower in the evening.
If you go to an air conditioned office and sit at a computer most of the day, you’ll likely want to showers as close to the start of the day and show up for the job as clean as possible.
I also think it’s easier for a white collar worker to get by showering at night than a blue collar worker to get by with showering in the morning.