I max Q all the time, though that's probably why I'm still Silver IV LOL
I think it gives him a lot of burst damage against the ADC, unless it's Graves. I've also been in many many situations where the ADC almost deals enough damage to get the kill and my Q can secure it. Happens a lot to me.
I've also been in situations where the lower Q cooldowns lets me keep the stacks up more often.
I max E second because I don't feel confident that my ADC will deal enough damage to get rid of the ADC.
I max W last because it feels like it's not as impactful as his E or Q.
But the practice is usually just habit of playstyle though. It does really good burst and if you decide to switch to a more harrass playstyle then it's more worth.
I recognize that I probably should max E in certain matchups/situations.