because they'll never have as good an opportunity as now. The big sides are in a bit of chaos (other than Arsenal who'll find a way to screw up before long) and a lot more vulnerable than they have been in a long time.
They are never going to challenge for the top 4 without a settled side and the players still adapting to the league and to each other. I think too much has been made of this season being their season. Man Utd, Man City and Chelsea had managerial changes but their players had played together for seasons and formed a good understanding. Spurs are regularly changing their lineups and AVB hasn't settled on his best side yet.