Competitive pressure. Gary Taubes in his books "The Case Against Sugar" and "Good Calories, Bad Calories" mentioned the competition between Kellogg's, Post and other cereal brands.
While it's hard to believe today, Kellogg's was founded by a health nut who was eager on bringing healthy grains to Americans. Once his descendants took over, they noticed how enriching their product with sugar increased sales. Kids specifically don't have necessary mental controls to recognize addictive behavior (which is why we have restrictions on sales of cigarettes and alcohol).
So bit by bit American breakfast table and grocery store cereal isle turned into varieties of concentrated sugar instead of the muesli, oats, granola and nuts mixes it was way back in the days.
As a (currently) flagged comment absolutely accurately notes, a major concern of the Kelloggs was matters of mental and spiritual hygiene, including concerted efforts (including surgery) to avert masturbation.
Medical historian Howard Markel addresses this in his recent book The Kelloggs, with some relevant aspects mentioned in this book-tour interview at KALW, Santa Monica:
[Dr. John Haarvey Kellogg] also was very chaste and reminded both his readers and his followers that sex outside of the marriage, of course, was not a good idea, but [that] sex for anything other than procreation really sapped the soul and sapped the spirit. And of course, he was very much opposed to masturbation of any kind, something he wrote about extensively and called "the solitary vice."
Ideologically driven reasearch in which conclusions are assumed or asserted rather than proven empirically has a poor track record for truth discovery.
The Kelloggs' theories of nutition are fairly hit or miss. Corporatising the institution they created has not helped.
While it's hard to believe today, Kellogg's was founded by a health nut who was eager on bringing healthy grains to Americans. Once his descendants took over, they noticed how enriching their product with sugar increased sales. Kids specifically don't have necessary mental controls to recognize addictive behavior (which is why we have restrictions on sales of cigarettes and alcohol).
So bit by bit American breakfast table and grocery store cereal isle turned into varieties of concentrated sugar instead of the muesli, oats, granola and nuts mixes it was way back in the days.