Note that none of this is official, and frankly anything that anyone is saying here has to be taken as speculation until official reports are released as the park has not said anything as of yet, nor have official reports been released.
However, having worked on the train, and knowing the people, processes and procedures, along with some off the record discussions with people that do have information and experience, I hope that I can offer a little bit of an informed guess about the train situation. I should make clear that I am not speaking in any way, officially or unofficially, for the park, inspectors, employees, or anyone that has worked or currently works on the train at Silver Dollar City.
First, I don't believe, and I expect the reports to confirm, that the train derailment was not the fault of any of the train personal- engineers, inspectors, etc. The work they do on the trains is meticulous- which I actually documented in a video I produced a couple of years back, and that includes daily track inspections. Furthermore, I believe that they will be cleared of mechanical issues actually being the cause of the derailment (though I'm not sure on contributing to what happened).
For those that don't remember, the area a week before the derailment was in a rather strong drought condition. It had been quite a while without rain. Then in the couple of days beforehand we had rain. A lot of it. Flood condition amounts of it. Lots of rain on very dry ground on top of rock (e.g. Missouri) can soften the ground and make it shift in a way that is nearly undetectable, particularly on a hill similar to where the train derailed.
The train had run without issue several times that day, and the issue happened near the end of the day, which means it was a condition that grew over the course of the day until the point where it actually caused the accident. They aren't checking that track after every trip, so if it's something that progressed, if there wasn't some sign of it they wouldn't have seen it.
I'm fairly convinced (and I'm waiting for the official reports to confirm it, which I'm fairly confident they will) that the cause was dry ground that had become saturated and then started slipping over the course of the day under the weight and strain of the operations that then caused the rails to displace just enough to cause the derailment.
That's something that is generally inspected for and worked on in the off season, as it's pretty much never an issue during the season. As witnessed by 55 years of it operating without incident, as well as all of the numerous theme park trains that have also not had a derailment incident like this.
To blame this on a "sudden failure of management" is uninformed at the best, and comes from a lack of knowledge of park and/ or train operations. And if that's you, I would suggest that you wait for official reports before speaking and speculating. :-)
That said, I'll step back into the shadows and let those that think they know better continue to speak. I've had other times where others tried to tell me how and what I and others did on the train, and I see some of that starting here again.