And just fyi not everybody can sleep in bunk..
Well, that is not the company's problem but yours. If you cannot do it and you feel too tired to do your duty, get a job where you do not have to rest in flight.
That is where aviation is going. Either you learn to prepare for a ULR flight to be tired at the right time and be able to get at least some sleep or you fly for LoCo's and do up's and down's the whole day but be in bed at a convenient time.