On an average, teams run somewhere between 105-120kms per game, which roughly comes out to around 10-12 kms on an average for a player (ignoring GKs). You rarely ever see a player cover 14kms or so on a consistent basis, which effectively means that effort of 1 player not tracking back and being given a free role can be afforded (which is what you see in every side), however, do that for 3 odd players and you then need a lot more workhorses.
If you have 2 or more players who think this way, the team will struggle quite a bit, especially in PL where fitness is crucial. Hell, in all sides where Ronaldo has been, the other players did help out quite a bit in defence including Benzema at RM