There are many types of transportation that elderly people can get if they can't drive (buses, taxis, personal services, etc). So making them free would deter the people who run the transportation services. I've already done a debate with the instigator of this opinion on this topic, if anybody needs further information.
They cannot drive because of eyesight, reaction time, arthritis, hearing and more. They need transportation for getting medicine, or pills from doctors and they can't do that without transportation. They don't have jobs anymore and all they have is a pension which won't get them a lot of bus rides