I can list some of reasons but it will not be a complete list.
1. Now US has a huge military base in Kosovo, Bondstill with
7.000 people deployed there. There is a joke that two things can be seen from moon with unarmed eye, Great Chinese Wall and base Bondstill.
2. Depleted uranium was used in this operation and other
forbidden ammunition. Just testing, you know .. on alive people. Corporations need it. sort of QA.
3. Just to show the rest of the world who has real power in this world and first of all to Russians. A way to say to everybody if you do not submit and shut up you will be next.
4. Destabilize EU and help euro crash. Euro/dollar exchange rate was not very good for dollar before operation but became after.
5. Get full control of Balkans finally and get rid of last regime which was not pro-Western in Europe.
6. Establishing a gangster state (Kosovo) in the middle of Europe which can be used for various purposes.
7. Like nr.2, testing airplanes, missiles and other systems.
Like I said this is incomplete list, I could add 2-3 items more.
Say hello to Atzlan.