The Stalinist government of the Soviet Union were big proponents of the accordion and did much to spread its use and develop its repertoire. The accordionistas are one of his greatest cultural legacies.
Why not accordion ?
To my point of view it's one of the most universal solo instruments, but not widely accepted in any classical or jazz orchestras or bands. It's also sophisticated. I'd say extremely sophisticated. In order to deliver smooth and artistic sound it may require long and extensive practice to handle bellows and position your hands properly. In addition there are two button boards that can deliver sophisticated polyphonic parts that can create an impression of small band inside one instrument. You can also count on fingers great accordionists while you can have an endless list of great guitarists or saxophonists.