Iver, for some people it is a matter of lifestyle. This is getting worse on the 777 as it picks up more of the bad flights (night turns to India, less desirable layovers etc.) from the shrinking 330/340 fleet. However, on the 380 it is still pretty good with more days off and mostly good layovers. If people have 30 years to go before they retire an extra couple of years waiting for a command may not seem that important if they enjoy the job while they are waiting. To other people a command as quickly as possible is all that matters.
Generally I find the former group less stressed!