Millions of grown men eat cereal because American advertising has bombarded them since the Kelloggs invented the over-processed abomination in the late 1800s.
Cereal, above all other things American, is an example of how you can deceive an entire nation with advertising lies. The whole cereal industry is as bad as tobacco, worse in that it targets children specifically with its ads and over-sugared, nearly toxic products.
The introduction of things like cereal and other American processed foods into the Thai diet is one of the reasons so many Thais these days are obese.
None of Earth's living cultures embrace a diet of highly processed complex carbohydrates for breakfast or any other meal.
People are willing to delude themselves that it is good for them because it is convenient.