That’s because the 1,000-mile road race was discontinued after a Ferrari 335 S killed its drivers and a bunch of spectators in 1957. It was revived in 1977, but as a regularity rally (traveling each leg in a prescribed time, not as fast as possible), so even customers could grace the historical event.
As for Mercedes-Benz’s offer, a racing driver will accompany the customer in the passenger seat as their navigator, helping them negotiate the routes like an expert and providing necessary assistance should anything untoward happen.
In completing the race, you’d be following in the footsteps of Sir Stirling Moss and Rudolf Caracciola, both of whom claimed victories in their time. Caracciola was first when he claimed victory in 1931 behind the wheel of a Mercedes-Benz SSKL – the original Silver Arrow – becoming the first driver from outside of Italy to win the overall race.