Well, maybe Croatia don't take this match serious
They did take this match seriously, didn't you see the squad? they used the entire first team minus Mandžukić. Every single team in the UEFA Nations League knew that this isn't your summer competition where you can relax all you want, this is actually an official competition where you play for the points.About Croatia, they were outplayed by a superior team, simple as that. This is Spain when they have a competent manager like Luis Enrique, not the joke they had in the WC with an interim like Hierro.
Btw, Iceland lost their two matches so they'll probably get relegated to League B where they belong. And Italy, did anyone watch their games? they are a complete disaster, wouldn't be surprised if they also get relegated to a lower league.
In case anyone wants to see the standings: https://www.uefa.com/uefanationsleague/season=2019/standings/
I'll agree Croatia did field a very strong team, but they were simply outplayed by Spain who're suddenly rejuvenated under Enrique. This is the Spain I once knew, free playing and scoring goals. I have said it before Italy has a long way to go, and one should avoid their matches. If they're relegated it's their fault, they're not putting in any efforts to play so in all fairness they should be relegated.
In the long run, these games matter, NT need play time, the coaches need their players every now and then so he explain tactics and whatnot and they need to see this stuff on the pitch aganist decent rivals, otherwise, we'll see shitty performance from them in the big stages (like Germany or Brazil in the last WC). 
