The Winter Solstice is the crux of the year. The sun was going away; now it's coming back. The world isn't going to end after all. We're saved.
The Summer Solstice on the other hand is just another nice warm day like all the others. There's nothing about it that packs any psychological, religious or cosmological punch. It doesn't relate to the agricultural cycle either. Think about it too deeply- this is the day that marks the beginning of the sun's journey into the underworld- and you could actually get a wee bit depressed.
The cult of high summer is a modern thing- holidays and beaches and turning brown for the heck of it. Our ancestors weren't into any of that. If they had choice in the matter they kept to the shade.
So there's nothing ancient or ancestral about the Summer Solstice party at Stonehenge. Not that I'm knocking it; it looks like fun. Good old King Arthur Pendragon, the Druid (I've got lots of time for him) was interviewed on the BBC but seemed a bit hazy when it came to explaining what he was doing there.
As well he might.
Because the Winter Solstice/Yule/Christmas always was and still is the one that matters.