Because the Nephelim were real and our true history is suppressed. There are a ton of old newspaper reports of giant bones being found. The Smithsonian (run by Jesuit secret society) always comes to swoop up the evidence and it's never heard of again.

The skeletons are there and their worldwide. Unfortunately the papers only ran the stories up to around the 1930's and then stopped reporting on it many of these skeletons had a lesser reported feature six fingers or toes. To dive into this rabbithole you need to go way back pre-flood. nephilim is an interesting subject of study and there is as you said worldwide legends of them.

Could be based on a residue of the childhood perception of adults as being giants who can do anything.

It's a common theme in lore that giants turned to stone. Also ideas of giant silica based trees being cut down.

As the Devil's Advocate in this situation, you could see the height obsession with a physical depiction of creatures larger than life. Or Governmwnts across the globe are trying to cover up the fact that there were giant humans back in the day.

Dinosaur bones, had to come up with some kind of explanation for them.

I think it's the wamens driving it, you know, "Big Feets.."