The other main reason newhires are offered 787 is that most of the existing qr pilots refuse to go to 787 for various reasons...
A lot of B777 pilots prefer to stay on their type for better destinations within qr till the 787 gets better network and dispatch reliability...As many still fear for another grounding...
Some qr A320 skippers prefer to get transferred to A330 and eventually to the A350/A380 which both are coming very soon...
Since the 787 is expanding a lot in the near future, there will be loads of slots for new hires...