Robin van Persie had a meeting with Arsene Wenger and Arsenal club directors earlier in the summer, which led to his releasing of a statement on his website where he stated that he would not renew his contract. In that statement, van Persie said, about the meeting that "it has again become clear to me that we, in many aspects disagree, on the way Arsenal FC should move forward." This was before the signings of Olivier Giroud and Santi Cazorla were finalized.
It turns out, van Persie was pretty happy with the signings, and was willing to stick around. According to David Ornstein at the BBC, van Persie was willing to stay, but Wenger had already started thinking about life after van Persie.
"It is understood Van Persie was encouraged by the arrivals of Germany forward Lukas Podolski, France striker Olivier Giroud and Spain midfielder Cazorla - to the point where he was open to the idea of staying with or without a new contract ... But Wenger pulled him aside shortly before Sunday's friendly victory over Cologne, told him he would be sold if a deal could be reached and informed the Dutchman he was no longer part of his plans. "
That might not sit well with too many Arsenal fans. It probably didn't sit well with van Persie initially, but he's probably getting over Wenger's decision quickly, since he's getting a big fat raise. The Telegraph, among other outlets, is reporting that van Persie's new contract with the Red Devils is going to be worth £200k per week.