Seems to me that you might not be so familiar with the industry of nursing homes, or of the mindset of the caregivers and nurses there. Before I start, I am NOT defending those caregivers - they're going to be fired and they will rightfully lose their certifications...but I've got some first-hand and legal experience in their world, and I have to say I'm not surprised.
First off, what you see there are almost certainly NOT nurses, but caregivers (who receive far less education than nurses). Nurses are held to a much higher standard and are normally (but not always) more professional.
Second, you know how crude the humor of soldiers and sailors can be, how we can laugh at the worst or most inappropriate things? Gallows humor, right? It's not much different in a nursing home filled with old people waiting to die. I don't know how much experience you have with caring for the elderly, but when we ran an adult family home, two of our residents had dementia, and one was a terror to try to take care of, while the other had no clue what she was doing. It's not unusual for a caregiver to walk in and find that a resident has painted the walls with ****, or has eaten their ****. Every experienced nurse and caregiver has a "**** story" - I have mine, involving a low-functioning autistic teenager. That was a fun day. Anyway, the point is, just as soldiers become hardened by the tragic crap that they see and experience, so also do the nursing home workers become hardened by the tragedies the see every single day. Sometimes they become bitter...and all too often, they become uncaring. Problem is, yes, they learn to ignore the suffering of their residents...but they often do so out of self-defense, trying to maintain a sense of sanity in a workplace where they serve people filled with sorrow and anguish and heartbreaking loneliness...and people waiting to die. That's why I told my sons that if they ever consider putting me in a nursing home, just leave me on the side of the road next to a forest.
Third, to make things even worse, most nursing homes are privately-run...which means that the owners find every way they can to cut corners on staffing and service. The nursing home with the best reputation in the county here is the one that's government-run. With the other nursing homes, you get what you pay for - the expensive ones (9K a month or more) give very good service indeed...but the ones where most people go are "state pay"...and the staffing and service, well, are slashed to the bone...which makes it even harder on the nurses and caregivers who do work there.
So...no, I'm not surprised at what they did. They deserve what's coming to them. But I also understand why and how they developed the mindset that allowed them to do what they did.