It's not so casual, nor is it about long-term endpoints. Every commercial consumer food product from large brands like this is the output of an elaborate, rigo

It's not so casual, nor is it about long-term endpoints. 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.