There's one main reason why.
It turns out Mercedes-AMG has been testing Project One prototypes at a secret testing site in England almost completely unnoticed. Every now and then a spy photographer or spotter may locate a test vehicle and snap some images or video, but that has yet to happen (as far as we know) regarding these specific prototypes.
However, the automaker has now acknowledged that keeping this testing site a secret is proving to be a more difficult task than originally thought. How come? Because of the Project One prototypes' unique engine sound.
Remember, the Project One, first revealed in near-production form as a concept one year ago at Frankfurt, is an F1-derived hypercar, technologically speaking. Mercedes-AMG says that "characteristic F1 sound they produce" is more difficult than ever to conceal from the public. That power comes from a plug-in hybrid powertrain that includes a 671 hp 1.6-liter V6 engine and four electric motors. One of those motors is built into the turbocharger, another sits in the V6 engine, while two more are located at the front axle.
Power, a total of over 1,000 hp, is distributed to all four wheels. Expect a 0-124 mph time of less than six seconds and a top speed of at least 215 mph.
For what it's worth, those electric motors will enable the hypercar to travel up to 15.5 miles on electric power only. The photos you're looking at were taken at the Millbrook Proving Ground in Bedfordshire. Unfortunately, Mercedes-AMG did not release an accompanying video so that we can at least hear that distinctive sound, but anyone who watches F1 races will know, more or less, what to expect.
Only 275 units will be built, despite over 1,100 requests, and all of them have been sold. Chances are not all buyers will actually drive their cars, but rather store them away as a future investment, which is a real shame because the Project One is meant to be driven.
AMG CEO Tobias Moers has already gone on record to say there's a good chance the Project One will be gunning for the fasted production car record at the famed Nurburgring, a title currently held by the Lamborghini Aventador Superveloce Jota. The Project One must be faster than the Lambo's 6:44.97. Given that the Project One (a name change is expected) now appears to be entering its final testing phase, an official reveal shouldn't be too far out.