Only 777s available?

We are booked on a multi-city trip in November (ATL-LHR and CDG-ATL, both through IST), and our return flight got rescheduled by 8 hours; we’ve been offered a complimentary change.

The problem is that EVERY SINGLE FLIGHT back is on the 777-300ER with the abysmal business class set up. I’ve gone forward and backward on the calendar, and I don’t understand how every single return transplant flight is a on 777.

This was not the case a month ago when we booked our flights, any idea what’s going on?