I'm not on the team involved in this, but I can direct you to some things that other (more relevant :) Rioters have said about the champ pick quotes:
RiotSocrates:
Hey dudes, we removed these from champ select. The issue was we had overloaded champ select with too many sound effects, making it hard to tell when key things were actually going on - like when it was your turn to pick. You'll still hear your own champ when you lock them in.
The upside of this is that since the recent patch we're seeing some of the lowest dodge rates ever.
And then to follow up on that,
RiotBoourns:
Right, and the problem is that the champion quotes can be pretty long and would actually stomp the "your turn to pick" sound. A further refinement could be muting the champion quote if you're picking next or fading it out when your turn starts. That was more complicated and we had some high priority fixes that we were working on so we kept it simple.
I do hear you, though, we all loved the champion quotes and thought they were a great way to add more flavor to the experience.
So it sounds like that team does love the champ select quotes, but in the interest of haste and getting a fix out, turned them off because they were stomping the 'your turn to pick' sound effect. Too many people didn't realize it was their turn to pick :( Looks like they might be able to revisit it when they have more time, though!