I recall there are receptors in your stomach lining which detect the presence of sugar even when its not obviously tasteable, such as in predominantly salty fast foods and so. This is a sneaky way to make you addicted while you don't even realize it.
Every commercial consumer food product from large brands like this is the output of an elaborate, rigorous "food science" endeavor that tests a variety of ingredient and preparation hypotheses against focus groups, established targets for texture/sweetness/..., cost, etc and balances those against any regulations that the brand's lobbying arm hasn't blocked.
They look for maxima across their field requirements and then send the results of that product research to manufacturing and sale.
Presumably, and unsurprisingly, they've found that sweetened milk drives more sales and brand loyalty and have therefore pushed it into any markets that allow it.
Sugar gives people a little dopamine boost. So if, as a company, you make your product a little more sugary, people like it more. Then, all the companies are in an arms race to make the tastiest product and you end up where we are.
Of course, it's not only about sugar. You also want to make it more salty and fatty because people like that too.
And somehow we can't stop this arms race that causes millions of people to have diseases like diabetes and costs society enormous amounts of money. I guess once Nestle buys up Pfizer and health insurance companies, the cycle is complete.
It was really annoying to make him eat ordinary porridge afterwards, so I guess the sugar is much about fooling the parents into believing the kid does not like the non-sugar product.
If you don't read the ingridients list you wont realize there is sugar.
A nurse once made him stop crying when he was to take a vaccine by sticking her finger in his mouth. I was flabbergasted by such a simple trick working so great, until she said she had sugar on the finger.
Sugar is a cheat code for parenting.
For adults salt and monosodic glutamate come into play, the logic is the same. The more you put in the product, the better it sells.