I am with you hvert ... I don't like to carpool. One thing I like about taking my own car is that I can come and go when I want to. I don't even get it for the 'company'. Their will usually be plenty of time for socialization when you get to the event. I am pretty comfortable now with telling people that I will take my own car.

So, in answer to your question, I really don't know why some people prefer to carpool even when it is illogical unless, like in the instance you pointed out where someone didn't want to lose their parking space, carpooling works to their advantage.

Like Nancy Reagan said - just say NO (and add a 'thank you' if you must )