Biggles, I would suggest that your motorcycle courier operation had riders all with invalid insurance - "hire and reward"?
If you allowed PPLs to earn moeny, how would you recommend that your customer distinguishes between you as a conscientious-and-just-as-good-as-a-CPL pilot, and a-wet-behind-the-ears-just-got-my-PPL-in-45-hours pilot? They can't. Or how about a new law which says PPLs can earn money ... but only on a good day
One aspect of a commercial licence is the monitoring of that licence through more stringent proficiency checks, operational checks and medicals.
Cheers
Whirls