Obviously racing is not allowed on public roads.
Ány sort of competitive element is suspect on the public road as just about all may motivate participants to ´compensate´.
This particular event, which is basically the rich flaunting their ostentatious cars in an organised tour, has totally deservedly had véry negative publicity in past events because of mega-high speed infractions, serious accidents, even deaths.
It is only because of the überrich & famous = the money & publicity involved, that the event has not been banned from public roads altogether. I imagine that the organisers are now very strict about control of the drivers. I don´t knów but it seems logical to fit out all cars with a gps tracker and automatically ban anyone being silly.