No it's not. It makes no sense to say "oh, you can't commute to work and then home again five times a week? so how do you get groceries?" because those are two completely separate things in completely separate environments.
It's none of Amazon's business how people manage their disabilities outside of work. The only thing that matters is what the most effective way of managing their disabilities is inside of work. Amazon is not your doctor, and if your doctor says that this is the most effective way for you to manage things while being productive then they need to accept that the doctor knows what they're doing.
Let's say, hypothetically, that someone gets this benefit who has no health condition that anyone will admit exists without being paid a bribe.
Are you arguing that you're taking something from the company by them allowing this?
You rapidly run into a similar problem to one many means-testing programs for benefits in the US do - it becomes far more expensive to do the testing than it would to just give people the benefit if they ask for it, even if many more people asked for it.
And if some core job requirement makes WFH an actual nonstarter (e.g. if you're being paid to move packages in a warehouse, you generally can't do that from your bed), then it doesn't matter if your doctor says you can't do it, they can still fire you for not meeting a core requirement of your job that they can't just work around.
Or, put differently, what's stopping someone from delivering WFH levels of productivity in the office, in this framing? If it's that they'd be punished for being unproductive, what's stopping that in the WFH parallel?
There's a lot of reasons to fire people if someone wants to, lots of things down to effectively what lens you view them through.
(This is not claiming that this is good or bad, just an observation of how I've observed employment in the US to go.)