They are testing more so for 'harder' drugs, particularly now that marijuana is legal. I certainly would never have foregone a 'smoke of the funny stuff' back home because of the possibility of it being detected when holidaying in Thailand.
Thailand was once semi lawless (in a real sense if not in theory) and a much better place to live in then than now. At least the Thais have taken a step in the right direction to improve the country's quality of life by legalising marijuana.
I suspect all too many of the local farangs are ready to pounce on any foreigners bending the law while ignoring the fact that Thais are the ones who act most irresponsibly on the roads in their own country.
Lol. Plenty of bikes wherever you go are on the footpath or heading up the wrong way of the road. I doubt that many of the riders are ever apprehended.