They did get Istria and western Slovenia after war, but even though they got invaded by all their neighbours, except Greece and Romania (who only gave Germans land pass for toops for the invasion) they somehow didn't get to occupy Carinthia or bigger part of Veneto region for example.
Regarding why Yugoslavia did not get to occupy Veneto, or other parts of Italy, so does it come down to that Italy was not carved up the way that Germany was. The reason for this has been discussed by u/AlviseFalier in this thread.
Regarding why Yugoslavia did not get to occupy Carinthia, or other parts of what had been Germany, so is it rather because Yugoslavia were not one of The Big Three; UK, USA, and the Soviet Union and could not convince those three that they should take part.
The original arrangement was that only those three were supposed to split Germany up between them. However, Charles de Gaulle worked hard on being allowed to take part and by the time of the Yalta Conference had he managed to convince Winston Churchill to propose the creation of a fourth zone for France.^(1) I cannot find any evidence of that Yugoslavia, nor any of the other seven European Allies, wanted to take part in the costly occupation of Germany; so France rather stands as the exception that confirms the rule.
Hence, the blunt answer to your question is that the UK, the USA, and the Soviet Union never intended to split Germany up between all European Allies and therefore did they, with exception for France, only keep it between themselves.
1 http://docnum.univ-lorraine.fr/public/UPV-M/Theses/1994/Perrein_Engels.Helene.LMZ9412_1.pdf