Why is magnesium oxide always recommended by doctors while it has the lowest absorption rate of all types of magnesium? why not chelated glycinate?

Magnesium: Magnesium glycinate is a chelated form that tends to provide the highest levels of absorption and bioavailability and is typically considered ideal for deficiency. Magnesium oxide is a non-chelated type of magnesium and is less well absorbed. Why magnesium oxide is often prescribed likely has to do with its lower price and stool softening properties.