I believe that's an Australian WR-450F advertisement from a few years ago.
In the USA, a WR-450F is not sold as a street-legal bike as it comes off the dealer's showroom floor.
In Australia, the WR-450F enters their country and is then equipped with parts to make it street-legal, and then sold to the end user (customer).
The guys adding the street-legal parts are either the Yamaha importer, or somebody approved by the importer to do this.
Either way, the laws allowing this to happen are definitely more relaxed than the ones in the USA where Yamaha Motor Corp., USA (as well as Honda, Kawasaki, and Suzuki) would be worried of a lawsuit (and a lawyer getting involved) if someone were to get into a wreck or some other situation where somebody was injured, killed, or incurred damages from riding a dirt bike on the street.
I believe this is why you don't see street-legal dirt bikes like a WR-450F sold in this country, and after the lawsuits of the 3-wheeled ATVs and the resulting ATV consent decree from around 1988, I really doubt they feel like risking it.