It's a basic that in safety situations that you have to have order, and keep things ship-shape.
In life generally: "anything not explicitly forbidden is allowed". But that is very much NOT the case in safety situations:
In safety situations it's very much the case that "only things explicitly allowed, are allowed".
One could state any whacky suggestion of something that is "not explicitly ruled against" in flight (such as "I want to do a hand-stand!") - you can't do them.
In safety situations there's a blanket idea that "you can't do weird shit," as well there should be.
As a curiosity: some friends of mine let their kid sleep on the floor (in front of their seat as you describe) on a Swiss flight about 10? yrs ago. The staff were incredibly angry and it almost reached the point of alerting the authorities on arrival.
(I do not know if "sleeping on floor" is explicitly forbidden on Swiss. But why would it be, or why should it be? "Anything unusual" is forbidden in safety situations.)
So the simple answer to your question is "you must keep order" in such a dangerous situation as a flight.
Here's an interesting example: If you literally just move around an awful lot during a flight - constantly walking up and down each aisle - you'll be told to cease and sit down.
If I was on a flight where the cabin staff were allowing people to sleep on the floor between aisles, I'd get someone important and try to have the situation corrected.
If you literally want someone to list the dangers of sleeping on the floor as an exercise...
(*) Obviously you need to, generally, stay seated during the whole flight so that if you need to go to an emergency position, you're as close as possible to that situation.
(Note that this is precisely why they tell you ......... to stay seated during the whole flight!)
It would be madness if, when the captain declares seat-belts-on, or even an emergency, the staff had to run around and find everyone sleeping on the floor and have them get up and sit in their seats!
(*) In case of sudden turbulence, being seated properly (even with no belt) is spectacularly better than being laying down sleeping on the floor.
(*) Note that indeed, if you are laying down there, your face is inches from a whole lot of sharp steelwork, bolts etc.
Indeed, simply, laying on the floor between airlines seats (I mean, when the plane is parked at the aircraft factory) is just not sensible or safe - it's not somewhere body parts are meant to be.
(*) Further to point (i), if you had ten people asleep as you describe and there was an emergency, 8 of them would get tangled (clothes or body parts) on all the stuff down there in rushing to come awake and get back to a seat.
In general ..
(*) The reason they say "remain seated for the whole flight" is obvious! its the safest if sudden turbulence, and, the quickest to get to strapped-in if there's an emergency
(*) It's just an outright bad/rather crazy place to be (get scratched, caught, your hand flops out in the aisle while snoring, scalding liquids tipped on you, etc etc etc)
I hope this answers your fun hypothetical-like question!