Because humans do not have enough time to eat plants or meat all day the only time efficient means they have to get calcium that I know of are
1 Milk
2 Lots of Chia seeds
Any other plant I know of will make people painfully to full
3 Calcium supplements or food with Calcium artificially added to it as an extra ingredient like Calcium fortified orange juice or soy milk or tofu
@shortstories @Stahesh Green leafy like spinash, kale lettuce etc are a good source of calsium
You can not eat that much Spinach or Kale
Do the math and figure out how large a volume that is
If you can then you need to start Vegan eating contests and win money for first place
@Stahesh @VeganMGTOW
Other animals eat for many hours more per day than humans and can digest calcium containing foods that humans have trouble digesting