As someone has posted, filling the 767 is a lot of work during the off season months. Getting an even bigger aircraft would cause a problem.
I have flown on LOT Polish Airlines Boeing 767-200ER/300ER and they definitely need to take care of them better.
Some seat pockets are broken, or just non-existent.
Some seats do not function properly and are not able to be returned to the upright position.
The panels are all yellow and disgusting from the days when people could smoke onboard.
Some of the projectors and monitors don't work.
The list goes on and on. With a bit of care, these aircraft could be like new, unfortunately this is not the case.
Unfortunately I'll most likely be travelling on one of these aircraft again on my trip to Poland in the summer. I doubt anything has changed from two years ago, and if it has, probably to worse.