Not enough money for something new, I guess. There is a contract for A319s which is not good for JAT and some terms had to be re-negotiated with Airbus. I don't have enough details, so I won't post much about it here.
The problem with Airbus and JAT is also that it is a completely different and unknown technology for JAT and buying planes would also mean training crews for new planes and it takes a lot of money, too. It is still unknown what JAT would buy, but it is more likely that they will get some of the Airbuses.