I'm sure that the 'habitual sellers' have never realised either that the are doing people out of jobs, commands and a more stable roster due to incorrect crewing ratios!
Actually I think most of the habitual sellers realise it only too well and don't give a monkeys. The way things are at the moment aircraft would be parked up but for people selling days and whole weeks of leave, as you say it's a sorry state for a company to be in caused by sorry management.