It seems to boil down to poor timing so often here.
They usually look when pulling out onto a road, but only as they are doing it, so it's too late. They indicate when changing lanes, but only as they are doing it or after, so it's too late. They look when they pull away from the side of the road, but only as they're doing it, so it's too late.
Off topic but a new roundabout is being built to replace some traffic lights here in Mahasarakham. That should be fun, since most Thai drivers don't seem to know how they work.