I'll take a guess. Yamaha and Onkyo are readily available on the internet at discount prices. Marantz (and Denon and Pioneer Elite) is sold primarily through A/V retail stores and, consequently, has higher street prices. The Saul Marantz name alone sold the products a generation ago but apparently isn't working for this young crowd. Denon appears to have the "quality cache" at the moment.
Personally, I view all of those brands as equal in terms of performance. I think Onkyo and Yamaha represent better values at the street prices for which they sell. Since I have no use for a local dealer to choose and supply a receiver, I have an Onkyo. I don't think it is any better. I do think it is a better value in terms of performance for the money spent.
All these boxes are made somewhere other than Japan where the parent companies are located. They all use similar components and, sometimes, are made in the same factories right next to each other. I wouldn't spend a lot of time worrying about the brand. Better to choose the features and performance level you want and shop for a price that works for you.