https://www.sciencealert.com/mysterious-king-arthur-monument-found-to-be-over-5000-years-old
I doubt if we will ever find an answer to this. But is it possible there is not only an astronomical purpose and an astrological purpose to where this is situated? A one of a kind structure that archaeologists know of so far, no doubt it is also on the ley line that runs through the area, which would mean its location is very important for either of these purposes. Whomever built this would have knowledge of such things to build here if this is on a ley line. Ley lines are the earth’s chakras being a living entity no different to any living beings.
Regardless of that ancient history is an amazing subject as is archaeology. I always find the UK an exciting place for both mystical and historical studies. I do miss my homeland when I read anything historical or even of the natural world and wildlife. Similar to Australia with magic in the air at sacred sites.
https://thetravellingwineglass.wordpress.com/2016/06/10/cornish-magic/
Here is a lovely article about Cornwall and the mystical history including Bodmin moor where King Arthur’s hall monument is located. I wish I could visit this place and enjoy the mystical atmosphere. Not to mention the beautiful scenery and wildlife.