Long range champions' damage is so absurd, who is not going to want to play mobile champions?
Champions who have long range advantages are so overpowered at this point that who would want to play non-mobile champions? Adc and mages do so much damage, what other choice do you give people? play a melee character and you're popped. Play any none meta tank and your cc into the ground. Your choices are super mobile champions or ranged champions. Melee champions are supposed to be the ones that do massive damage on account of the long range disadvantage, but since everyone now has pop you shit tons of damage why on earth would anyone not choose mobile characters? It's either get popped or try to be mobile enough to even have a chance at getting the kills. You still get shat on most of the time by cc and their damage, but at least you have a chance.
etc. Cause of course none of them have dashes, ms buffs, gap closers etc., but wait no they do. I didn't even count the cc users into this who just stop all melee champions. No they Don't need stupid fucking damage.
and 
she was so impossible to deal with for melee champions, that riot started to put a lot of mobility into new released champion kits.