Originally Posted by
UndedoKoleda
You can't get boosted, true, but other than that I believe that a huge part of the challenge to reach gladiator is the ability to be a team-player, meaning to be able to find partners, to know how to play given comp and to sync with your teammates. In other words, playing just your class is one thing, playing a particular comp is another(and sticking with the people for it), if that makes any sense...
Another possible reason is that if you can get same mount from regular arena and solo shuffle, many players might follow the path of least resistance and abandon the regular arena and focus only/mainly on the solo shuffle. Which could have a domino effect in participation and eventually "kill" the regular arena ladder.