There are any amount of theories as to the purpose of this, or any of the other Henges. Some sound plausible, some not. I’m reminded of the sketch in Dead Ringers, where they send up TT. Where Phil (I think) finds a piece of pottery, on the basis of this, they assume there was a large Roman town there, with temples mosaics etc (or words to that effect). At Durrington, how do they know that every hole was a post hole ? if they were post holes, how high were the posts, and how thick ? You cant tell the thickness of a post by the size of the hole. It’s possible the posts were only short, and forming supports for a fence . Perhaps it was an animal enclosure, and where animals were slaughtered for food, not to part of a ritual. Perhaps it was a defensive stockade to keep out marauding foreigners ?
The fact is, we’ll never know for sure.