Same argument as before. I could name you at least 10 defensive midfielders in the world that are better than Ramsey, easily. For a team that wants to be in the upper echelon of the world team, you need to have the world's best players playing for it consistently. Right now, Aresnal doesn't have even one player you could say that he is top 3 in his position in the world at the moment, and that isn't good enough to win the Champions League.
This year it seems like they are finally ready to spend some of the money that they have been making over the years by selling their best players.