Giants: Why Did They Become Extinct?

Painting 70cm x 50cm
Long Barrow Giant True Or False?
Things dug up from the past. This is an alleged giant from Long Barrow, Ireland. Was it authentic or a hoax?
Let your imagination run wild: giants might have been useful in creating monolithic structures such as Göbeklitepe or Stonehenge. Giants are mentioned in religious books. There are accounts of giant skeletons being found and allegedly removed and hidden by for example the Smithsonian Institution. Historical and archaeological finds have been chronicled and published by e.g. Forbidden Archaeology: The Hidden History of the Human Race 1993 by Michael A. Cremo and Richard L. Thompson:
http://www.mcremo.com/fa.htm

Conventional wisdom dismisses such ideas while an ‘alternative’ circuit of researchers and academics continue to probe the issue. The existence of giants is considered mythical, but what if there were such beings? It surely makes sense to at least be open minded to such contemplations, examinations and questions.
Smithsonian Admits to Destruction of Thousands of Giant Human Skeletons in Early 1900’s:

Smithsonian Admits to Destruction of Thousands of Giant Human Skeletons in Early 1900’s