Because the cost of fuel in the EU is quite high, and a lot of people commute long(er) distances on a regular basis instead of flying.
It is considered an entirely acceptable system because the "cost reimbursement" will fully cover the cost of wear + tear + fuel, meaning that a drive across the country can be rendered effectively free for the driver.
Also, "without any income for the driver" isn't necessarily correct - if you have a full car you will make a tidy profit.
Edit: the cost of a blablacar trip to a passenger would be on the order of 13-16 euros for an hour's drive. Comparable or cheaper than a train, with more flexibility.
It is considered an entirely acceptable system because the "cost reimbursement" will fully cover the cost of wear + tear + fuel, meaning that a drive across the country can be rendered effectively free for the driver.
Also, "without any income for the driver" isn't necessarily correct - if you have a full car you will make a tidy profit.
Edit: the cost of a blablacar trip to a passenger would be on the order of 13-16 euros for an hour's drive. Comparable or cheaper than a train, with more flexibility.