This we would have to ask the NATO directly. One reason could be that the western world has a conflict in deciding whether or not the Balkans form a part of Europe.  If the Balkans do not form  a part of Europe, then it is not tolerated for a foreign part to use arms on our borders. If the Balkans are a part of Europe, then it is not tolerated that a member uses arms within our boundaries.
So this means: we cannot accept the use of weapons close to our areas of interest, except from countries such as Turkey, that are under our control and reasonably distant. Accordingly, the NATO interventions are not an humanitarian act, but an action with at least the plan to follow geopolitical strategies.

No western youth intends  to die in a war. On the contrary, in developing countries and in the former socialist countries there exists a firmly embedded violence and a vision of life and death that differs from the one of the industrialised West.
What is called fanaticism or "consciousness of premise" (Bateson, 1979), is to die for ideals, whether they are right or wrong. The only way seen by NATO to avoid a direct confrontation between human beings that could lead to thousands of deaths, is to count on diminishing the moral resistance of the 'fanatics' with the terrorism of bombs and missiles.
But does it work?

Since the Second World War it has been shown that military attacks using on a large scale air force and battleships work only in territories free of natural obstacles, as the French and Russian plains, the North-African desert, etc.
In Cassino, Italy, in 1944, the bombardments that destroyed the medieval abbey, did not provide any solution. A small group of German parachutists was enough to keep the position untill the landing at Anzio threathened a flanking movement. During the second world war the campaign in Italy was marked by the inefficiency of the means of modern war. The territory taken in two years (June ‘43- may ’45) turned out to be of minor relevance compared to the advances of the Russians from the  east and, later by the Allies from the  west (June ’44 – may ’45).
Moreover, different from the situation in Iraq, the people in the Balkans believe in combating in order to defend themselves from a foreign invasion that aims at cancelling their national identity.

The word ‘Serbs’ is almost unknown to modern Westerners since the Serbian nation as a national unity has been cancelled after the first world war. The Yugoslavs, on the contrary, are better known, for their resistance movement  to Nazism during the Second World War, strongly supported by the British. During the resistance Italian and Yugoslav partisans operated together-despite all of the arguments that have arisen  in the last few years.
Then, in the years of the cold war, Yugoslavia broke up with the Soviet Union, remaining outside  of the two blocks and  elaborating political initiatives to constitute a pacifist block of third-world countries, known as the ‘movement of the non-allied countries’.
Subsequently, Yugoslavia has been a travel destination for many Europeans, and therefore there exists a direct acquaintance with its people.By using the word ‘Serbs’, the ex-partisan, the pacifist, or simpler, the waiter and the taxi-driver we have got to know some years ago, all disappear. Instead of them we speak of an ethnic entity that we cannot clearly define and therefore it’s easier to attribute negative characteristics to them.
This trivial form of  action has been efficiently used by the USA during the second world war towards the Japanese, calling them  ‘yellow monkeys’ (as they have also done with the native americans calling them ‘redskins’), in order to dehumanise them. Konrad Lorenz (1969) calls this process ‘creating pseudo speciezation’, or the intent to attribute to one's rival characteristics typical of another species to remove the natural inhibition of inter-specific violence. This trick, extensively practised by the Germans against the Jews, can also be used applying simple differences as cultural or linguistic diversities etc.

In the Balkan wars massacres and deportations of defenceless civilians are considered from an historically point of view as a common  practice. This, however, does not necessarily mean that this is happening presently, just as we have not to leap to think that the German army involved in the current operations behave as they did  in the past.
That deportations of civilians happen is a fact, as probably also mass executions happen. But then why, regardless of  insistent  requests from part of their own allies (e.g. Germany) there has not yet been given any proof of such massacres? Why do  the news agencies speak of deported and murdered  ‘males between 15-50’, and yet show on TV  a  homogenous population of refugees, with both genders and all ages present?

The tactics of the army and the militia of Milosevic, certainly promoted by the bombardments of the NATO, has probably had the intent to dispel the population momentarily to deprive the UCK-guerrillas of their logistic support.
An inhuman operation which we have seen in the  recent past used by the USA  in the Vietnam conflict. Once the guerrillas have been eliminated  the population can go   back.