From a playing perspective where are they going to go to and will they be undisputed starters? We are not going to sell too Chelsea and United (I hope..). City invested in two young wingers (Sane and Moreno), Sanchez is not be a big priority for them and Ozil isn't either with Silva and De Bruyne. Juventus just signed Higuain and are set with Dybala and Higuain. Bayern has Muller, Thiago, Vidal and Robbery probably still have a couple of years in them, they have no immediate need for a winger or an attacking midfielder I think. Real is not going to buy back Ozil and Barcelona is not going to buy back Sanchez. Barcelona is probably the best option for Ozil, but still.
Not saying Ozil/Sanchez are lesser players than the alternatives other clubs have, although I think that goes a little bit for Sanchez, but winning trophies not included staying with Arsenal isn't that of a illogical option.