Studies prove otherwise:
Suboptimal magnesium status in the United States: are the health consequences underestimated?
https://pubmed.ncbi.nlm.nih.gov/22364157/
Subclinical magnesium deficiency: a principal driver of cardiovascular disease and a public health crisis
https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC5786912/
Where did you hear that “magnesium deficiency is very rare?”