Having asked around, I think 1000-1500 hours could be salvaged for learning each year, but this time is necessarily outside regular business hours and therefore not suited to many common retraining programs.
How can this demographic best use 1000-1500 hours, in a year, to attain a new career path?
They do this to precisely to try to ameliorate the hopelessness and exhaustion and to recover enough mental energy to face another day without going insane. Humans are not robots.
This comes down to 3-4 hours of focused effort, every single day of the year, on top of their work and family responsibilities. Have you actually tried living like this even for 6 months? I doubt it's mentally feasible for most of people.
I will assume you don't have a family to take care of + a full time job.
Seems like this issue is why folks choose to spend their time the way they do. It's understandable. But, there's no point in being like "XYZ is the way to go", unless we're talking about someone who is already motivated and already making an effort, but hasn't been able to find something that's right for them.
And I'd bet that's a minority.
Plus of course the answer would depend on individual circumstances.
I think it's good to routinely spend at least 1000 hours yearly sharpening skills at work and off duty.
Seems like it can give you a number of possible new career paths if you so choose.