[JoesBro]

Its all to do with "Sanuk" -the Thai philosophy of making the best out of everything life throws at the individual. My own personal theory is that if there is no food -it is not "Sanuk" !
Most of the food at these various festivals etc is prepared communally by those taking part - no outside caterers !!- so cooking, eating and sharing with each re-affirms the bonds that ties people and communities together in the good times and the bad times. Some village Wats keep a collection of large saucepans etc just for such mass celebrations. Everyone gets fed -even the spirits via the spirit house. Monks cannot eat after their midday meal.
Someone observant once said "Thais do not eat to live, they live to eat!" Another equally observant person also said "If Thais are not actually eating, then they are thinking of what they are going to eat next !"
The lack of a weight problem among the majority of Thais may be due to Thais habit of eating 4 or 5 small meals a day instead of of the several very large ones we westerners tend to eat. Their metabolisms have a chance to burn off the carbohydrates in between meals. Never the less, there are some obese Thais. What Thais tend to traditionally eat may also be important, some Thai children are becoming obese from constantly eating western junkfood.