There are plenty of situations where this might happen if they’re in your room: a lightning strike can cause a surge that causes the disks to fry, a thief might break in and steal your system, your house might burn down, an earthquake could cause your disks to crash, a flood could destroy the machines, and a sinkhole could open up and swallow your house. You may laugh at some of these as being improbable, but I have seen _all_ of these take out systems between my times in Florida (lightning, thief, sinkhole, and flood) and California (earthquake and house fire).
The fix for this is the same fix as being proposed by the parent post - putting physical space between the two systems so if one place become unavailable you still have a backup.