There have been some derailments on C&TS and on other narrow gage railroads, and they have ranged from mere one-wheel things that are only aggravations to serious derailments in the back country that caused injuries.
Does a responsible owner/operator wait until there have been fatalities and injuries? If so, how many deaths and/or injuries? How much property damage?
In a nutshell, C&TS has said they wil lmaintain the track. FRA wants (and has every legal right to demand) something to base this on. They aren't jamming anytuing down C&TS's throat, nor has anyone but a few extremists said anything about gold plating the railroad. That FRA is letting C&TS establish it's own standards says a lot. Once they establish them, all they have to do is live up to them.
All those who keep braying that FRA has no jusrisdiction should spend some of their own money for a lawyer to test that theory in court.