#3 Out of form players
This point is connected to the first one. You can't have good form when your players aren't performing well on the pitch. That has happened for both Madrid sides this season.
January can't come quickly enough for Atletico. They badly need some scoring punch with only 16 goals so far in 11 league outings. Diego Costa will certainly help them in that regard, but his second coming is still a while away.
Angel Correa is currently Atleti's leading scorer in the league with four goals. Antoine Griezmann, who had 16 league goals and 32 overall last season, has found the net just twice in La Liga this season. Defensive midfielder Thomas Partey has so far scored more (2) than Kevin Gameiro and Fernando Torres combined. As a matter of fact, he even has more goals than Cristiano Ronaldo.
Ronaldo scored his only league goal on October 14 in a 2-1 away win over Getafe. He's played in seven matches and has had 13 shots on target, so you can't say the likely Ballon d'Or winner has not had chances to find the back of the net. With his goals missing, Real has so far scored only 22 goals. That's eight less than Barcelona and Valencia.
Ronaldo's goal drought in the league is actually a bit bizarre as he has six Champions League goals in four matches.
Karim Benzema also has only one league goal to his name. Isco and Marco Asensio are sharing the top scorer honors for the club with four goals each.