I wonder why Sevilla did not do everything to take advantage of their chance to finish second in La Liga. The only explanation I can think of is that they are tired after the whole season. The situation was similar in Barcelona, when they lost the entire series of matches.
I don't think the reason is the fatigue of Sevilla players. Sevilla performance has decreased much since the middle of this season, how can those players feel tired very quickly? Doesn't seem to make sense as the reason. They may have an internal problem, or they have a problem with the tactics or player formation. So, Sevilla players cannot play comfortably, and hard to develop their game. While Sevilla has a problem with their performance, Barcelona and Atletico Madrid started to improve their performance in the second half of this season. So, they gradually can overtake Sevilla from the 2nd place. Well, it is very unfortunate that Sevilla wasted the chance to be the runner-up, they may no longer have the same opportunity in the next season.