Of course you don't drive on the shoulder all the time. At times you have to move out to the middle lanes. However, when I do it, I look in the mirror, throw a glace over my right shoulder and safely merge. Most Thais? They don't look. They'll just pull right out in front of a car going 20, 30, 40 kph faster than them. It's suicidal, just like pulling out from a side road onto the main road without looking - which I'd say 80+% of Thai M/C do. It no wonder 80% of the fatalities are M/C.
When I had a "Big Bike" I drove like I did in the US except I never found it fun driving here at all as you can never let down your guard for a second and just enjoy the ride. Driving here is like driving in an Arcade Game.