There were several factors to account for conversion, but the main one was that the culture of the Albanians was much more suited to Islam than to Christianity.
First of all, the rebellion of Skanderbeg in the 15th century infuriated the Pont, so after he was finally defeated, they made a special and determined effort to convert the Albanians to Islam. This gave them a toehold for the later growth in the country.
The main factor, however, was the warlike nature of the Albanians. Albania is a mountainous country and the people there have always never been simple farmers. They have often lived by sword and have a long tradition of being mercenaries, just like Skanderbeg. The style of rule there is "mountain chieftain" where each valley and hill has a mini warlord, who, in many cases ruled very tyranically over the locals. This political reality was much more conducive to the nurturing of Moslem tendencies over Christian ones. Even when Albania was a "Christian" land, they were notorious for being very fainthearted about it.
Another big factor is that the Turks kind of loved them for this. While the Turks treated other captive nations contemptuously and meanly, they loved Albanian military style and often hired them by the thousands as mercenaries, who were called Arnauts. Turks even dressed up their little boys in Arnaut soldier outfits, like we used to dress up boys in cowboy outfits. The Albanians were kind of the "Navy Seals" for the Turks. This created a bond between the Turks and Albanian chieftains who were heavily Moslem.
Ultimately, the upper classes and property owners in Albania became so dominantly Moslem that they were able to forcibly convert the whole country and this was done en masse.