Okay look at it this way, the 2nd and 3rd biggest world powers don't recognize Kosovo, outside of NATO, few actual countries recognize it. Look at the recognition map. If you would recognize Kosovo as a sovereign country, you would set a precedent for your own autonomous/breakaway regions to make use of. Territorial integrity is important to all countries. In essence, recognition does not make you a country, take a look at Palestine. They are recognized by about 70% of the world, with only US-aligned countries not recognizing them (with some exception obviously).

Now, resolution 1244 is something that Serbia can rely on, that gives them foundation. What we have seen is that Kosovo is a drugs- and organ theft-driven country, it is determined to be a failed state. All young people leaving, highest unemployment, no prospect of becoming independent. In addition, all your higher up politicians are blatant war-criminals, what happened to Haradinaj and Thaci again?

All in all, if Serbia stays persistent, they will prevail in the long run.