Why do people max q on LeBlanc?

It is for waveclear. If you max E, you're going to get shoved under turret all game once your opponent realizes you're doing it and you won't be able to roam, which is LB's strong suit.

BEcause W got gutted

Maxing E got quite a while ago, and then recently her W got completely gutted (mostly good for movement now), but her Q bounce dmg on minions got buffed. So her play style has changed to maxing Q to help wave clear and CS better. You can still max E, but i would only do that in match ups you KNOW you are going to win

As a LeBlanc main who never maxed Distortion first even before she was reworked and is always maxing Q first, I got so used to Old LeBlanc doing the W Q R combo. Popping the max level old Sigil of Malice gave guaranteed damage.

Most people maxed W because you can just keep on jumping and jumping and also that was her only form of waveclear together with Mimic Distortion if a single W wasn't enough, but then if you're not going to use it to damage champions, it's gonna hurt because it costs 100 mana at rank 5. With New LeBlanc, before her W got gutted, it was still the same W because it had decent damage, but even then I still max Q first to poke having to W first for the new Sigil of Malice, then a few AA's hopefully proccing Thunderlords. Luckily if you get a chain too then more damage.

So since i'm maxing Q first, the consequence for me would be the long cooldown for W, but the lower mana cost (80) isn't bad given i'm also using mana regen seals. Also the plethora of cdr from Morellonomicon, Abyssal and Hourglass really helps me from the W cooldown suffering xD

Now with the huge nerf to her W, now it even more suits my playstyle as I've always been just using W for gap closing. Even more of a buff for me because Q was just buffed. :)

So for me, Q is not just for the waveclear, it's also for a good harass. ^_^