EL AL is a privately owned airline. They have already done their calculations, and decided that their future does not involve a 7 day schedule. It is rumoured that when the 'unofficial' religious boycott of EL AL was running recently, they were losing in the region of NIS 1m per day. The increase in passenger numbers would have to be very substantial in order to offset both the loss of religious passengers (many of whom are very frequent flyers on prime routes) and the additional salary costs involved in hiring workers for Shabbat.