For the same reason most electrical machinery incorporates a big red button called an emergency stop. The use of the fuel cutoffs is dictated by the flight operations manual, its its function remains the same regardless of thrust lever position, weight on wheels, power output, speed or angle of attack. Adding another permissive for fuel cutoff valve operation increases the potential for other potentially disastrous events. It is one of the things a pilot does, like flap settings, not turning right on a taxiway when there is a lake on that side or retracting the landing gear when crossing the threshold on approach.
Well then, clearly, it is a design fault. Should you actuate the emergency stop on an electric motor…….you don’t instantly kill in excess of 200 people nor destroy a multi million dollar aircraft.
Fuel cutoff’s on turbofans should be designed for starting and stopping, engine fires, volcanic ash ingestion resulting in flameout, severe compressor stalls and runaway engines. Not when you are attempting to get a fully loaded 787 into the air. The software, as per other aircraft designs, should prevent fuel cutoff at takeoff thrust. Simple as that.
At flight level, the TF’s are running at somewhere between 20%~40% full thrust. Fuel cutoff to one engine, for one of the above reasons, is perfectly doable.
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They build them like the customer wants just like the 737 max which forced the use of Mcas
Good call moderators making a new thread 
Around 14:57 of this video there is some general info on these switches on a 787. Including what they are connected to. They are monitored in the central alarm/control/monitoring system as well as acting directly on a fuel valve. It also explains what component was actually replaced in the past and why operation is a manual action and not linked to throttle lever position or engine state.
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So the logic in this fuel cutoff toggle switch design is primarily to prevent uncontrollable thrust which could damage the engines and this “logic” is held by both Boeing and Airbus (20:11)
Strange logic.
Other, smaller, aircraft manufacturers hold and practice a different logic whereby the cutoff switch(s) is/are incorporated into the thrust levers and the levers must be brought back to the idle position, lifted over a detente prior to activation of fuel cutoff.
This particular “logic” has resulted in total destruction of both engines (not through uncontrolled thrust), total destruction of the aircraft and the loss of 260 innocent souls.
What’s this "total destruction of both engines " by “uncontrolled thrust” thing?
A gas turbine can be destroyed by excessive exhaust gas or turbine inlet temperature but belief in “too much thrust” or a “runaway” engine is truly bizarre.
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So the logic in this fuel cutoff toggle switch design is primarily to prevent uncontrollable thrust which could damage the engines and this “logic” is held by both Boeing and Airbus (20:11)
Strange logic.
We Mariners can’t cover ourselves in glory here either.
How many times have you ordered half ahead to watch the engine start then slowly spool itself up to 50 rpm as the load programme kicks in.
The logic is protect the engine even at the expense of the entire ship. Stupid Stupid Stupid.
When on OSV s we often had a run overide by pressing that button we knew the engine was going to be destroyed , that, as Captain was my choice and if it meant saving my/ our lives I would not hesitate to press it
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First on an OSV I cannot imagine a situation as you describe unless it was poor watch keeping. Second, if you destroy an engine in the air it has different consequences from destroying a boat on water. Likely the boat won’t sink, guaranteed the airplane will.
Very simple
Working up wind/tide
Using high usage of power.
Port engine decides it needs to shut down due to a failed lub oil pump
I need that Port engine to stop my vessel getting ripped to shreds on the teeth of a jack up.
So press that button and survive .
I have done the doggy paddle in the North Sea in a Force 9 so do know what it is like for a Jack up to rip you to bits after a machinery failure.
Oh sorry missed your last comment as I was a bit annoyed
Yes the ship did sink
I was master on one of Reg’s Rent-a-Wrecks that had patches over where the teeth of the jack up rig had pieced the hull in the fire pump room.
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I will nail my colours to the mast now.
It’s time to remove the warm body from the front of an aeroplane.
I can quote many many examples when pilot incompetence smashed an aircraft into the ground.
I am prepared to hear , other than the Sully example, when a warm body at the front actually saved the plane
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It does get my goat when I hear constantly about autonomous ships when they never address the simple issue of how to throw a heaving line.
It has been proven that a F18 can land on a carrier.
I must admit a big hole in my argument is how does the plane get to the threshold. Maybe a warm body could taxi it there then jump out 
DP vessels all got kills at the console, runaway thrust is a serious issue.
Qantas 380 out of Singapore when the engine exploded and being full for long haul computer said cant land, Pilots ignored all that crap and said we need to be on the ground regardless forget the check lists and the thousand alarms going off..younger pilots following the rules would have binned it.
Used all 4k of the runway…
PS as the computer wires were cut to outboard engine, it landed with port outboard engine at climb thrust and couldnt shut it down.
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Wow, what a masterpiece of applied training, experience and, most of all, mental discipline under stress…
They had been “overstaffed” like this, because a senior check-pilot was present to supervise a check-pilot in-training. Admirably this cluster of old salts did not result in stalemate/ inaction. As a warm-bodied passenger, I would have been very grateful that the flight computer was overruled…
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