Parking
It probably is just down to laziness as they don't want to park 5 miles away
(slight exaggeration) and catch the bus to the terminal, which can be an ordeal in the early morning.
I pre-paid LS1 two weeks ago and was stopped at the barrier by a very nice man from NCP. He asked me if I would like a free upgrade to Multi-Storey 1, as LS1 was rather full and we would be parked miles away!
By the time I had turned around and got parked on the 4th floor of the multi I had not saved any time but of course not wanting to pay the rip-off trolley charge it was very much appreciated due to the short walk to and more importantly from arrivals on our return.
Also to cap it all due to a tech aircraft and a longgggg baggage reclaim I had over-stayed my 8 days (as mentioned in an earlier post) by 20-30 minutes and NCP were fine.
I must admit I tend to park in the spaces provided, not on double yellows as I would hate to give anyone the satisfaction of giving me a ticket!!! However someone rushing for a flight if delayed in traffic will no doubt take their chances. I suppose worth the risk especially if someone else is paying like your company.
Pete