Tito managed to keep Yugoslavia on reasonably good terms with both the Western and Socialist blocs (in later years at any rate, he was the subject of much invective from other communist states in the late 40s and 50s for not toeing the Stalinist line).

In particular he was one of the founders of the Non-Aligned Movement a group of nations that seek to be independent of any major power bloc. It includes such countries as India, Iran, Indonesia, Egypt, most African and Middle Eastern countries.. So you can imagine a lot of presidents etc wanting to be at the funeral.

There must also have been the motive among the Western and Soviet blocs that they should try to influence the new Yugoslav leadership into leaning more to their side than the other- this was 1980 after all and the cold war was getting chillier again after the Soviet invasion of Afghanistan. So sending the highest level delegation you could made sense politically.