Well, obviously calcium supplements are supposed to deliver calcium, not a bunch of other compounds. Also, they avoid mentioning that there are a considerable number of plant milks and similar products that are fortified with calcium and other nutrients such as vitamin B12 and vitamin D. They also avoid mentioning the many other sources of phosphorus, including many nuts, beans, and seeds. Furthermore, as the Harvard School of Public Health concludes:
“We cannot be confident that high milk or calcium intake is safe”[29]
The same publication also notes that:
“There’s no good evidence that consuming more than one serving of milk per day in addition to a reasonable diet (which typically provides about 300 milligrams of calcium per day from nondairy sources) will reduce fracture risk. Because of unresolved concerns about the risk of ovarian and prostate cancer, it may be prudent to avoid higher intakes of dairy products”[29]
And it goes on to mention that:
“For individuals who are unable to digest—or who dislike—dairy products and for those who simply prefer not to consume large amounts of such foods, other options are available. Calcium can be found in dark green leafy vegetables, such as kale and collard greens, as well as in dried beans and legumes. A variety of calcium-fortified foods, such as orange juice, cereals, and plant-based milk (soy, rice, almond), are also available in most markets”.[29]