The problem is that the government deregulated commercial aviation several decades ago... so while they do retain control on some aspects, they may not (yet?) be legally permitted to set slots for KORD without new legislation being passed.
Hence, the meeting was purely voluntary and in my personal opinion, a bit of a waste of time.
The laissez-faire model of commerce essentially demands that 'the marketplace shall respond'.
To that end, the commercial airlines are loading up slots and gates as much as they can.
It would be in their general best interests to have a smooth and efficient overall experience, but yet, they don't want to give up hard-fought or hard-earned gates or slots since it would just be yielding market share to a competitor.
So if we had the government step in... the various airlines would scream foul, big time, because then there's the question of how do you fairly reduce slot allocations in a manner satisfying to all?
But ultimately, I'm in favour of slot restrictions to set an upper bound of what can indeed be handled most of the time (the 82% on-time percentage the FAA wants sounds reasonable to me).
There's difficult questions "between here" and "there" -- such as persuading the legislative body (the U.S. Congress) to pass additional legislation enabling the FAA to impose slots restrictions, as well as coming up with a mutually acceptable scheme for imposing a reduction in slots amongst the various airlines.
So, right now, the FAA believes all it can do is to request the airlines cut back and raise awareness of the issue so that the legislative body might be favourable upon the idea of imposing legislation to control this.
This, however, runs contrary to the marketplace-decides laissez-faire approach of the current government administration. So... it's not clear right now what the government wants to do and what they're willing to do, and the airlines are loathe to willingly reduce slots on general competitive principles...
So, essentially, they're in a bit of a pickle as to how to best handle this.