Politics. Nothing more. And wishful thinking.
Fact is that Croats, Bosniaks and Serbs are more similar to each other (almost same) than many of their nationalists care to think.
All of them are descended from Balkan native tribes (Illyrians, Thracians and Dacians) mixed with Northern invader tribes (Slavs, Germanics and Celts), with Slavs and Illyrians being by far most dominant in make up of their peoples.
So fact that some Croat and Bosniak nationalists claim to be Illyrian, Gothic, Sarmatian (Croats), Turkish (Bosniaks) and anything else other than Slavic is only partly correct, but why in hell would they be speaking Slav language then?
But I think this stupid movements are starting to die off, no?