Because what I see is people do one ultra-crunch week, and then shout "OMG I work 80-hour weeks!" as if it was the normal occurrence, when the reality is they're working ~50hrs on average.
Again, people do it but it's not useful. Once you back yourself into a corner, all you can think about is moving one foot in front of the other no matter how inefficent the path you're taking is.
From there the only thing that will stop you is some outside factor, because you no longer have the clarity or discipline it takes to stop.
If you're lucky some great windfall from all the inefficient work you're doing will be that outside factor, but most likely the outside factor will be your health failing, or interpersonal relationships failing, or everything failing anyways because you aren't even at 50% effectiveness to make up for the 2x time you're putting in.
I've done periods of what I call "sleep/work", where I wake up with my laptop next to my head, immediately start working, and work all day: definitely not leaving my house and usually only even leaving the room to grab deliveries or use the restroom. I'd work until I literally couldn't stay awake, with the laptop next to my head and ready for when I wake up to continue. So literally for entire days I'll have done nothing but sleep and work, with even eating being done while working.
You can certainly do it, but it's an (unproductive) expression of mental illness that will additionally worsen every facet of your existence in short order. Elon's definitely mentally ill too: either for doing it regularly or being enough of a sociopath to claim that others should do it on his behalf.