I think its to encourage someone to buy whos more commited, but might not have enough money upfront to purchase a F1 team normally. Ford did the same when they sold Jaguar, they sold it for a token $1 provided the buyer could secure future funding and support for the team.
In comparison, look at the sales of Jordan and Midland and both times the team sold for tens of millions, but there wasnt any money left to develop the car.