I think a critical component of the problem is not only lack of vitamin D3, magnesium, vitamin k2 (essential for shepherding calcium to the bones), all necessary in calcium synthesis, but especially the type of calcium used.

The cheapest and most common form of calcium supplements is calcium carbonate. Calcium carbonate is essentially a rock of calcium, a form that cannot be used by the body to build bone, causes calcium deposits in the body and tissues...because the body has no use for it, and this buildup and interference disrupts body processes and promotes cancer.

The best form of calcium to use is calcium citrate. You definitely should not use calcium carbonate, or calcium from oyster shell or bone meal which are just calcium carbonate by other names.

JMO.

My supplement protocol/day for bone-building:
600-1200 mg calcium citrate (600-900 for maintenance, 1200 for building)
100 mcg vitamin k2
400-800 mg chelated magnesium in divided doses
10-15k D3

Weight bearing exercise is critical to building and conserving bone, but weights need to increase over time...that's how bone gets stronger.