I myself have never understood this either, whenever i go to a beach and theres tons of room around, ill set down all my stuff and then half hour later a family will come and plonk theirselves right near us, argh so aggravating, especially when theres loads of space to choose from!
Thats why when i see the pictures of Brighton beach or Bournemouth etc in the newspaper when its been a really hot weekend, and the beach is sooo crowded, people practically lying on top of each other (oo-er!) that is my worst nightmare, how is that meant to be fun or relaxing!!
But i must say in Arillas ive never had this problem, seems people like their own space as much as i do.