debra - that's one of the most evocative and beautifully written postings I've seen on the forum, and it sums up so much.
We also ask "why?"
The village itself is not pretty, is it, in terms of little old buildings (none), narrow twisty streets (none), Hellenic ruins (none)? Parga has many of those, but the harbour stinks and it's lethally expensive. Lindos is very beautiful, or was until they surrounded the wonderful old centre with hectares of sweaty tourist dwellings. Tolon was quirky and close to Naphplion and Epidavros, but greed has killed the village by building new blocks along the edge of the beach.
Agios Stephanos has the great advantage of geography and geology. We all laugh at the triumphalism of the Romanza dwellers gazing down from their Olympian heights, but it's those hills that make the difference, I think. The village sits, being its own modest self, between the big ridge towards the north and Avliotes, and the dramatic headland that divides the village from Arillas. Wherever you are you can look up or down, get some perspective, enjoy the light. And the beach is so huge that, as you say, there is never a sense of being crowded.
It's only a few miles to Sidari, but when you're there on that flat plane it seems to me featureless, desert-like compared to Agios Stephanos, where there is always a green vista in the corner of your eye.
And then, of course, the people. Friendliness can be simulated, but after a few visits you get to know people, you get to hear things you wouldn't hear in Parga. I don't think we have an word for "lack of greed" but if there is one it would surely apply to the tavernas and apartment owners. I have never felt ripped-off in Agios Stephanos apart from the fruit and doughnut man on the beach.
Finally - I think this forum keeps us connected with the village all year round. A bit of gossip, how's the road going, who's had a baby, now much is a Mythos this year? I've hosted a few forums and I can tell you it is hard work with constant idiots and bots and crap, and takes a lot of hands-on to keep working.
I suspect we've all fantasised about having a little house on the edge of a beautiful Greek bay. Why do we go back? Because we're so much at home it almost feels as though we have.