It's still popular in Europe. My brother used to race Sidecar. I think he still has his. He built one with a 600 ninja motor. He did Pikes Peak on it modified it with weld wheels and BFG comp t/a . I know some guys that did Dakar on Sidecar.
And their passengers, not monkeys!
Used to see them race before the US Grand Prix at Carlsbad Raceway. Somewhere in a closet I got some pics of them from the late 70's. Those guys are loaded with testosterone