My guess is they suspend the net out of concern for the equipment. There's now two discussions going on with this thread. One is the possibility of being hit by lightning while driving a vehicle and the other has to do with the things we do to protect our radio equipment during an electrical storm.
My personal preference is to disconnect everything from the rig to isolate the rig from nasty weather. On the big towers, all transmission lines, power lines, and rotator cables are disconnected at all times with all the transmission lines dead ended in surge protectors. All of that will probably prevent lightning from damaging my equipment. It won't prevent lightning from hitting the house.
Lightning is bad news to the radio operator, especially if concerns about it aren't a part of the radio equipment installation.
1966 FJ45 LWB Pickup
1985 BJ74 RHD