Traditional guidebooks: Thailand is a predominantly Buddhist country as these figures show: Buddhism 95%, Muslim 3.8%, Christianity 0.5%, Hinduism 0.1%, other 0.6%. As devout Buddhists, Thai people partake in the act of making merit which shows awareness and has positive outcomes as it leads to good karma.
Guru's updated version: Thais are Buddhist because it is definitely the most chilled out religion. You don't have to go to the temple every week, there's no need for any real fasting and we are tolerant of other religions too (we love going to church because the songs are so cute). But don't ask us what any of the Buddha days represent because how are we supposed to know that kind of stuff? However, if you want to come back as a luk krung in the next life you ought to regularly give an offering of Mama noodles and tinned sardines to monks. It's that simple.