Apologies for my limited answer, but it's a bit late where I am. I might try and expand a bit tomorrow.

I can't speak for the Albanian conversion to Islam, but in Bosnia it's to a large extent explainable by the Bosnian Church's relatively weak position due to the Great Schism. Bosnia was, very generally speaking, the borderline: to the West and North, including Croatia, it was Catholic, while to the South and East, including Serbia, it was Orthodox. The Bosnian Church was sort of caught in the middle and ended up excluded and rejected by both sides, and so was very weak come the Ottoman conquest, and its adherents subsequently more susceptible to conversion.

There was a similar question a while back, so I'll link to the answers there

I don't have much to add, except that a similar answer is applicable also to Romania and Bulgaria. In short, it would be strange if there were very few conversions. They were, however, much more widespread than it is often remembered.

I answered such a question a few days ago:

The Ottomans had a policy of not forcing religion, but many inhabitants in newly conquered regions did choose to convert to Islam. The most prevalent regions for this were Albania, Kosovo, Bosnia, Crete and north-eastern Bulgaria. While the expansion of the Ottoman Empire continued up until 1683, all new lands would have had Muslim populations to some extent. For example, the modern day area of Slavonia in Croatia is reported to have had some 50 mosques, while the area of Dalmatia in Croatia also had Islamic influence up to the regions held by the Venetians. One example of this is the old town of Vrana, held by Jusuf Maskovic, an Islamicized Croat. So, beginning in 1683 the Ottoman Muslims in the black regions on this map were expelled. In Croatia, Hungary and Transylvania, it is believed that most Muslims went to Bosnia, northern Greece or were killed/converted. As for the orange regions on this map, they fell in the 18th century after the Peace of Karlowitz in modern day Sremski Karlovci, Serbia. The Muslims in these regions were believed to have mainly gone to Bosnia, others were converted and killed. There were many Ottoman Muslims in the Bessarabia, Yedisan and Podolia areas corresponding roughly to modern day Ukraine and Moldova. With Russian imperial expansion (which was really the main cause for the persecution and destruction of Ottoman Muslims) these lands were invaded and the population (mostly Nogai and Crimean Tatars) are believed to have gone to the Dobruja region of modern day Romania and Bulgaria, from where many went to Turkey and others were assimilated into the modern Turkish population. Then comes the Greek war of independence in 1821, whereby the Morea region became independent. There were many Muslims in these regions but all were expelled during the war of independence or massacred. A notable example of this would be either the Navarino or Tripolitsa massacres. So, by the mid-19th century, there were no more Ottoman Muslims in the Morea, most had gone to then Turkish-controlled Greek Macedonia or Western Thrace. Then we get to the Serbian uprising in 1830. Again, the Muslims from the Sanjaks of Smederevo, Uzice and all in Karadorde's new state seen here. These almost all went to Bosnia or to Turkey. Ivo Andric wrote about these refugees in his book Cuprija na Drini. So, the next big thing were the Balkan Wars of 1912-13. The main victims of this were Muslims who were from modern-day Greece, Bulgaria, Macedonia and Montenegro. These became well known as muhacir, and almost all expelled went to Turkey (Istanbul, to be precise), as they had nowhere else. During this period, Bulgarian and Montenegrin Muslims also fled to Turkey, as did Cretan Turks, mostly to the Aegean part of Turkey. After this, the 1923 population exchange made sure that Muslim areas in modern day Greece (Crete, Larissa, Thessaloniki, Kastoria, Ioannina) were expelled of Muslims who were in turn traded for Turkish-speaking Christians from Anatolia, one example being the Karamanlides. Hope this helped.

If you're interested, here's a map of Muslim percentages in Balkans in 1877

tl;dr, many Serbs, Croats, Bulgarians, Greeks, Armenians and Georgians converted but were over time ethnically cleansed or forced to convert.