Because it has a significant impact on your family life, social life and your health. When you’re on days doing Mon-Fri and get the weekend off you get a full Satuday and Sunday. When on nights doing Mon-Fri and you get the weekend off you get Sunday as the only full day off. And whilst you get the same number of hours off half of Saturday is spent asleep until dinnertime, Monday you’re just burning time waiting to go work. So effectively you get just one full day off.
But like I said if you CHOOSE to do night work you should take all that into account-same as trampers choose to tramp even though it affects home life etc.
If nightwork affects you so badly why do it 'cos in my book the extra money was no where near enough to tempt me.