Below is what Arsenal is saying, but I believe it has to do with Nigeria being unstable with security issues here and there, guess they probably dont want to just come out and say "We are not coming to your Country because of Boko haram"
Arsenal marketing director Angus Kinnear said: “Bringing a top-level club to an international market is always complicated and logistically challenging. With the proposed match in Nigeria planned for early August, we could not get comfortable on everything needed to satisfy our requirements, so we have reluctantly taken the decision to postpone the team’s visit.”Kinnear continued: “We have a huge and loyal following in Africa, and we are sorry that the team will not be visiting this summer. However, we have a long-term commitment to Nigeria and we are already making plans for a visit next summer.
“In addition, we also have some exciting forthcoming activities planned with our commercial partners in Nigeria – Emirates, Airtel and Malta Guinness, which will kick off in the next few weeks