Simple
mob exp raises
card exp % most high level people have 50%+ so add it on a weekend and technically you are running genius (without having genius)
lvl 99-106 is the exact amount of exp to level so takes less mob kills and new gear offers better stats and boss damage which allows more exp from factions, invasion, mystics, posi etc per turn, and also the new higher bosses offer a lot more exp when killed, which you save till the weekend and open when you get the extra 50% bonus. Most people also wait till there faction has capped its exp, if its possible to have a mystic at that time built and also with Genius to max the amount of exp you get from boss links.