It's difficult to pinpoint exactly what Keter IS these days. In the past it was "Safe won't kill you, Euclid might kill you, Keter will kill you", and that was pretty easy to go by. However, after awhile there was a huge influx of "THIS THING IS SUPER DOUBLE KETER IT WILL KILL YOU TO DEATH" objects that weren't all that good and were only there to be cool and to stand equal with 682.
I remember those days, and so do a lot of people, so there's a pretty intense knee-jerk response to Keter objects that kill you. Unfortunately, this also hampers a lot of legitimate attempts at making a good Keter SCP. Hell, I've seen several really good Euclid SCPs that could easily be Keter.
Me personally, I don't want to write Keter SCPs because I just don't think I can make something believably dangerous without it being over the top or stupid.