It is a leap and mistaken assumption that going from concertmaster in a top orchestra to a solo career is necessarily "moving up". As Brownsfan points out "a steady job in a world class orchestra may be a better fit" for an individual; this could be for a variety of reasons.
First of all, the life of a soloist is not all that it may seem to be. Constantly traveling is very difficult on the person and that person's family, and different individuals will have different levels of tolerance to these difficulties. As musicians, some have more of a team-player mentality (to their credit) and find a great deal of satisfaction in the role of leader of an ensemble with the special relationships that are established, not only with the other players and instrumental sections, but also as liaison between these players and the conductor; a particularly important role in our age of constantly changing guest conductors. Additionally, and perhaps most importantly, soloists are often limited to performing certain solo works over and over again. As concertmaster a player can truly have the best of both worlds: playing in a top orchestra and performing all the wonderful orchestral repertoire, and also perform as soloist with that orchestra and (fairly regularly) as guest soloist with other orchestras; many do this quite successfully.
First of all, the life of a soloist is not all that it may seem to be. Constantly traveling is very difficult on the person and that person's family, and different individuals will have different levels of tolerance to these difficulties. As musicians, some have more of a team-player mentality (to their credit) and find a great deal of satisfaction in the role of leader of an ensemble with the special relationships that are established, not only with the other players and instrumental sections, but also as liaison between these players and the conductor; a particularly important role in our age of constantly changing guest conductors. Additionally, and perhaps most importantly, soloists are often limited to performing certain solo works over and over again. As concertmaster a player can truly have the best of both worlds: playing in a top orchestra and performing all the wonderful orchestral repertoire, and also perform as soloist with that orchestra and (fairly regularly) as guest soloist with other orchestras; many do this quite successfully.