Maybe it could be because the Athletico Madrid players were still tired after they played against Real Madrid in the Champions League so I think it is natural that they had to experience defeat when facing Barcelona even though we know that Athletico Madrid could hold Barcelona to a draw in the match but unfortunately because in the final minutes of the match the concentration of the Athletico Madrid players began to lose control and made their defense weaken so this is what caused the Barcelona players to be able to win the match with a very convincing score.
That's quite reasonable, the Atletico players seemed quite exhausted after their intense match against Real Madrid in the Champions League, causing them to lose focus in the final minutes of the game. Diego Simeone certainly needs to fix his team defense, which looked very fragile. Overall, they are still on track for the title race.
Barcelona still has a postponed match against Osasuna, which is scheduled to take place in the middle of this week. They will most likely secure full points again, as on paper, Osasuna is certainly easier to beat than Atletico. If successful, Barcelona will lead the top of the table with a 3-point gap from Real Madrid.