I'd agree with you that just due to the differance between the number of cars/trucks vs number of motos you would have to be correct. I would add that in my experience, in LA County, if I pull over 10 motos I've found that generally one won't have an endorsement. If I pull over ten cars at least three wont have a license or will have a suspended or revoked license which is as good as not having one at all.
A possible reason for this is because motorcycles tend to be viewed as pleasure vehicles. People buy them for sunday ride in the hills(yes, I know a good number also use them as their own daily driver). People with pleasure vehicles are more often up to date on their license because the money needed for said pleasure vehicle would not be as easy to come by with no license. A car is viewed as by many as a tool to get to/from work or a tool to complete a chore. There are some who feel it's better to just gamble with the idea of not getting caught then paying their fines to get their license unrevoked or getting car insurance.
