Herding Instinct?

It seems to be happening more and more frequently, we drive into a fairly empty car park and park somewhere where there is a fair bit of space so that parking is easier and so that we can fully open the doors and exit the car with more ease. We went for a carvery, parked as I describe above and before we could even get out of the car two other cars had zoomed in and parked either side of us. There were LOTS of other spaces but I suppose they felt more secure nearer to us?
The same in Tesco. Loads of spaces around our car when we went into the supermarket but dozens of cars clustered around our car and loads of space in the rest of the car park when we returned with our shopping!
Then, at the doctor's surgery on Monday, there are PLENTY of vacant seats; two separate groups of vacant seats in fact. Duncan and I sit down. Two other people come and sit one seat away from us. Another person comes and sits next to us. There are about 15 vacant seats in the other group! Then two people come and squeeze into the only vacant seats next to us! Why? Is it our personal magnetism? Warmth? Or is it the aforementioned herding instinct?