I know he's just another travel blogger, but this guy did a lot of reaching out to the city and other airlines as part of the linked article. The long and the short of it seems to be that the "preferential" gate distribution between tenants gets rebalanced in October for usage based upon the prior year (they apparently start looking at it in Feb). So it makes sense why the recent summer schedule increases have been announced at American.

His take: "What DOES matter is that this is all a silly shell game anyway. Remember, the gates don’t change over until October 1, so United will only get to use those six gates for the last three months of the year. But when the process starts all over again next February? It looks at departure share for all of the previous year. That means United will not have the benefit of those six gates for the first nine months of data which skews things greatly. That means it could very well lose again next year even if it is ramping up. And the cycle will continue since the data will never include more than a quarter of a year with the most recent gate allocation."

United Says It Grabs Six More Gates at O’Hare, But It’s Not Entirely Clear – Cranky Flier