It's actually more like dumping fuel for an emergency landing instead of dumping passengers, if we really insist on using completely irrelevant analogies.
Incidentally, fuel dump systems were initially added due to a rule by the FAA that a plane's structural landing weight not be exceeded by its takeoff weight. Many commercial planes never had this problem, so dumping systems were not installed. As a result, most planes just circle until they've burned up enough fuel, or land anyway overweight. You could dump fuel to lessen the chance of explosion, but only if your plane is equipped with a fuel dump system, and such incidents are so rare it's not even a safety consideration.
"Why not just plan ahead? Because most of the time, it was a very abrupt failure that we couldn’t detect with monitoring."
So you have a system, and you have monitoring in place. Let's say the monitors were set up for 1 minute polls, because somebody thought that was a good idea. Suddenly you find out one of your servers is down. Oh noes! There's 45 seconds until the monitor finds this out, which would be horrible.
Since we have doubled the reads on the existing servers, we now no longer have capacity and connections are stacking up. Shit :'( But not to worry! Let's just quickly kill the extra reads - now we have more capacity! Hooray!
Except, if the extra reads weren't happening, they would have already had extra fucking capacity and not had to flip a switch in the first place.
Now you see why i'm mad, bro?