I feel it is a double edged sword with CM Immigration. They can be sticklers for paperwork but on the other hand they are the most helpful immigration I have dealt with in Thailand - and I have dealt with Jomtien, Chimchurri One Stop Shop and Bangkok main immigration.
UK licence number. 42 million car licences and 1.2 million active motorbike licenses. This is probably similar to most visotor countries. Most people do not have a bike license or endorsement to allow the riding of bikes in Thailand
You do not seem understand the concept of what the IDP is valid for. If no bike license at home then not valid for a bike in Thailand. The vast majority who bring an IDP to Thailand do not have a bike license at home. This is pretty simple. Is it beyond your ken? In your observational studies have you not been establishing the endorsements? You need to setp up your game.
Chiang Mai is not that large so getting to Bangkok Hospital from anywhere is not an issue. Nimman is one area where many foreigners live in apartments and condos - not many houses there.
You call BS on everyone else so returning the compliment. I commended you on your observational study from the comfort of your barstool. Will you be upgrading to a randomised study? PS: How do you know the people fined had a motorbike endorsement on their IDP? What was your sample size?