Because it is a drastic simplification/elimination of a process I personally have no difficulty with and often find satisfying to carry out, to whit the use of a manual gearbox and clutch to drive a car and a braking system to stop it. The more simplified a process becomes the more the phrase "a child could do that" comes to mind.
Now I can understand that those who can't cope with a manual gearbox, those who get no pleasure from using a manual gearbox, and those who's journey involves nothing but nose to tail traffic needing or at least preferring an auto box, and the one pedal system is just an auto box with the inclusion of "automatic braking". (Yes I realise manual cars have a small amount of retardation off throttle, but it isn't something I choose to rely on.)
You yourself have highlighted a significant problem with that sort of system in that you are relying on the regen braking to slow the car, and it may not be sufficient for the job. Unfortunately by the time you have realised that it may be too late, whilst those who expected to use a footbrake would already be braking as necessary. I suppose it's the same as "self driving" - by the time you realise the system isn't going to cope you may be too late.
And the hand crank starts it just fine with a little extra exercise thrown in.
I really enjoy driving a standard transmission sporty car, but everything else is better with an automatic in my experience. Still haven’t tried one pedal driving, but looking forward to it.