Nothing to do with their old religion. Janissaries were the ones mainly from Bektashi order. As more Albanians started to be recruited into ocak, more of them allowed to return back to their hometowns either to keep people from rebelling or due to old age, and more settled back with their new religious sect. That's how Bektashi order gained a foothold in Albania. Once Atatürk closed down every sort of religious order and sufi lodge, Bektashi orders in Anatolia caught under crossfire and left the country for Albania.