The question has already been answered several times. In short, Bosnia and Albania aren't special, population of Serbia, Bulgaria and other Balkan states also converted to Islam. During the 19th century liberation movements most muslims in those states were killed, forced to convert or forced to leave. Belgrade up until Serbia's independence was a majority muslim city, with almost 300 mosques. Now there is one. Montnegro used to be majority muslim up until late 1600's when "Investigation of Turklings" was commited by Montenegrin tribal leaders who exterminated or converted trough force most of Montenegro's muslims.

As such, Bosnia and Albania are not exceptions due to conversions, but due to that population surviving. Albanians managed to create a state for themselves, while Bosniaks benefited from major Serb losses in WW1, which forced Serbs to try to assimilate rather than exterminate local muslims in order to replenish their own numbers (Serbia lost half its male population in the war)