When Tyson and Cargill give rides to their illegal immigrants, they don't get taxed on that benefit. A self-employed business man deducts his expenses which might include a fleet of vehicles. So, why do employees have to pay tax on a vehicle that is used for getting to work and back?
If your employer provides you with a car and you use it for other things than business use, you pay tax on the non-business use. Commuting to and from work isn't business use.
This is because most American individual taxpayers will not be able to document what portion is used for work and what is for personal, and even if they can, it is too much work for the IRS to track that it wouldn't be economically feasible for them.
If allowed, this type of deduction will have everyone trying to claim it, and without good documentation. It will never happen.