Inspecting the league table tells you everything about why Liverpool and Arsenal have failed to launch a title challenge this season. The points column shows Arsenal 13 points behind Chelsea (with a game in hand) and Liverpool a further point back, but the "goals for" and "goals against" column illustrates precisely why.
League leaders Chelsea have scored 55 goals, the same number as Liverpool. Arsenal, meanwhile, have scored 54 goals, and considering they've played one fewer game than the others, this means they're effectively scoring at the highest rate in the division. Going forward, both sides don't have many problems.