The big guys only work because they offer a range of products, not only aircraft and fast cars, but horse riding, quad biking, hot air balloons anything you can imagine.
So when people are thinking "what shall we get dad for his 50th, he's got everything he needs" then they look there for inspiration.
A site featuring only aircraft and fast cars would not work, as people who know that they want aircraft or fast cars will go directly to the people who supply them, who will be able to do so cheaper as they will not have to cut you into their profit.