I guess it’s because they are waiting for all aircraft to be converted. There are only two more aircraft to be fitted and one of them is already in the hanger. As the converted aircraft have 12 extra seats in the same amount of space it is easier to keep the seat maps at 36 seats until all aircraft are flying with 48 seats. If you have travelled on a 3 class aircraft before I think you will find the new seats and configuration is much better, well the crew prefer it.
CIHY