The game between Mallorca and Girona ended in a surprising outcome because there's no way anyone expected Mallorca to win Girona after they have been doing so well in the La Liga and winning all their matches but I guess you are right they didn't take the match seriously maybe because they want to focus more on the La Liga where they are currently topping the league instead of losing concentration playing the copa de rey which can actually affect their performance.
Yeah there are several reasons for Girona's defeat but whatever the reason I still can't believe Girona missed this game even though they are only a few steps away from reaching the final, maybe Mallorca's 3 goals in the first half surprised the Girona players so it has an impact on the player's mentality this kind of thing often happens in several leagues. Luckily I didn't watch this match, because if I had watched this match I probably would have bet on Girona.
Girona missed an opportunity to lift a trophy this season after their direct rival, Real Madrid, left the race early in round of 16 in Copa del Rey and after also Barcelona defeat by two goals to four against Athletic Bilbao. The first half was heavy on Girona and although scoring two goals in the second half and facing only ten players, Girona couldn't get the draw.
I think Bilbao will have a good chance in this trophy unless Atletico Madrid overtake them. I doubt Real Sociedad could maintain a good performance until the last game if ever they reached the final match. I don't think also that Mallorca could make another team leave this competition.