Because football is a sport that's hard to judge using statistics. Even the advanced stats that clubs have are unreliable; raw stats that are available to the public are largely misleading because you need context. Pass completion rate for example have lots of variables like distance, defenders in between, pressure the passer is under, pace of the pass, movement of the target etc. Also take a look at their PL best XI so far. Patrice Evra, who has been dreadful this season, made the team, and they have Gerrard there too.