Wenger offered him a contract worth 180k/week to stay. He's just lucky Liverpool are even more stupid.
Where was that offer reported? Unless Wenger or someone at the club has confirmed it I have a hard time believing it. 180k a week would make Ox our highest earner by far, everyone else is under 150k. No way Wenger gives that to someone who's never scored more than 6 league goals in a season.
Wenger is also all about squad harmony, its one thing to pay Sanchez and Ozil far more than the rest of the other players. But imagine giving Chamberlain 180k and going into contract negotiations with the rest of the squad. Majority of them, who have scored and assisted more than Chamberlain by far, will demand at least parity.
They might all be professionals but imagine how the likes of Giroud, Ramsey and Koscielny would feel, knowing that they have performed week in and week out for the team. Then seeing someone who's contributed very little to the team in terms of goals and assists making almost double what they are on. At least Rooney had the past six or seven years of high level performances to justify his wage at the time, even though it turned out to be a colossal mistake. Ox has done nothing to justify that type of wage offer and giving it to him, may have negatively affected morale. Hard to believe that Wenger didn't come to a similar conclusion.
That story reeked to me of Ox's agent trying to: 1. Make it appear that Ox is a lot more valuable than he is and 2. Endear his client to Liverpool fans, by demonstrating that his client "rejected" a large offer to go and play for them.
Moreover why would he reject 180k to go and accept 120k or so (I could be wrong) from Liverpool? The smart thing to do would be to say "Well Arsenal offered me 180k, so I want 150k to sign here, because wages are increasing and I'm a valuable young English talent." or something to that effect. No agent worth his salt is going to arrange a move for his client where he earns 60k less than he could make somewhere else, when said client is now entering his prime footballing years.