Basically it all stems from lack of law enforcement,plus many of these kids grow up in rural areas where it’s accepted. You won’t change a thing until the police start confiscating bikes and fining the rider and family. Until that happens,nothing will change,just another day in Thailand. Same has to be said about zebra crossings,pulled up at one yesterday to let the person cross the road. Nearly got rear ended,the car past me on the right to avoid hitting me, No one else stopped in the outer lane so I proceeded with caution. The person who wanted to cross the road just waited until there was a big enough gap in traffic for him to cross.
So your dammed if you do and dammed if you don’t. Just like roundabouts,they honestly have no idea on how it’s supposed to work. They stop on the roundabout to let you enter,people here just don’t really give a flying F.