The problem with a directive like this is that it will more likely hurt the genuinely sick and disabled rather than deter those that know how to navigate the system to their advantage.
The other issue is that when you look at the jobs market as it is today, it's obvious that a lot of it is low-paid, menial work (possibly also exhausting work) with unregulated hours which make it difficult for anyone with family commitments.
Germanshepherdsmum says that work is the best option if you are suffering from depression. For me this was also true - but that was because I had a good job which was relatively well-paid, and a sympathetic work environment, all of which was conducive to me making the effort. The fact that my manager "understood" made it all the easier to get out of bed in the morning, join my work colleagues, and be part of normal society. My GP - the same GP I'd had for many years, knew me - encouraged me to work but would've signed me off if he thought necessary. I'd already had a home-visit from a psychiatrist (unheard of now) who was 'encouraging' and, in short, I felt I had people on my side so didn't feel isolated or desperate, and it had a huge effect on my recovery.
Compare that with how things are now...