Is it because prices are cheaper - probably not. It's just a lovely exerience. You stroll around, generally in the sunshine. You may meet people you know - and because of the throng, you can avoid people you know and don't want to meet (or is that just me) - and you soak up the ambience. You can buy most everything you'd want:-
Ste Foy la Grande, the nearest big(ish) place to Villeneuve has a Saturday morning market:-
You can even buy livestock:-
You can have a meal with friends, whilst watching the traffic go by:-
And you can buy things you never knew you wanted:-
Oh, and here's a picture of my dog, Molly the Collie.