Why so many newbies on night shift?

I just recently switched to day shift after having spent almost 3 years on night shift. As was customary, when I was hired in as a new nurse, I did my orientation on day shift, and then was transferred to nights. At the time of my hire, nights had a pretty good mix of nurses with experience and new nurses with under a year of experience. Over the years more and more senior nurses moved to days, while new nurses went to nights. Three years later, the balance on my unit on nights with experienced nurses v. new nurses is very unequal. Although I am no longer on night shift, I do wonder now how safe it is to have a unit staffed with entirely either new nurses, or nurses who may have some experience, but completely new to the unit.

This seems to be a common practice in hospitals in general, but why? I know that seniority allows nurses who have worked at a place of employment longer the first choice for days, so I understand why nights is overrun with new nurses, but it's not a safe practice at all. We now have nurses with less than six months experience about to be trained for charge duty. The blind leading the blind. This also causes increased stress in these nurses, and the turnover rate increases and the cycle starts all over again.