Management. When you have management who have never worked the floor, it becomes very, very apparent that they have no idea what's going on, what the daily work consists of, etc.
No advancement from within, new management staff brought in instead of looking to promote existing staff.
Hugely clique-ish environment; management have favorites and don't hide it in any way. Certain staff can just make up things that didn't happen and report others they don't like. Not uncommon at all to see staff threatened with firing for daring to have an idea on how to make something better.
Overworked staff especially during the pandemic (a pandemic management were painfully slow to respond to, firstly stating there wasn't one, then knee-jerk overreacting with draconian responses) , not uncommon to see staff crying, taking extended time off for mental health due to lack of compassion from management.
A 'culture of mediocrity' - instead of trying to improve, mentioning that rooms weren't restocked, animal weren't graded is met with annoyance from management that it has been brought to their attention, rather than trying to fix the basics.
During the pandemic, communication between staff collapsed, to the point that the only way of letting people know what had been done, etc, was for a mass text chat using your own personal devices, which degenerated into memes and photos and was almost impossible to use, with staff being complained at by management for _using_ their phones.
It is hard to imagine a more harmfully toxic workplace, and certainly I have never seen one, nor wish to.