Are Croatia just not interested in this thing then?
Well, Croatia and Balkan teams are extremely hot and cold in general.
Croatia's world cup was a surprise to some extent, knowing our mentality.
The last time when Croatia achieved big things, in 1998, we we were playing horrible in the qualifiers after that and didn't qualify for Euros 2000', ending behind Ireland and Serbia.
Croatia lost motivation and it will take some time and some heavy beating to get back on feet, since currently we probably think that the opponents will be scared of us and that we will win just because of who we are.
Spain, on the other hand, had a terrible World cup, they have a new team, a new coach, a fresh start, a lot of motivated youngsters, and everyone wants to play 120%.
Mix those two things, add a lucky goal or two, and a match can easily end 5:0, 6:0, 7:0 or similar.
This is a perfect example of what happens when your motivation is drained from a (too) huge achievement.