Isn't this how it's handled in other countries when someone can't work due to medical issues? Surely they have some way of discouraging fraud, probably by making the doctor responsible or perhaps requiring multiple doctors to cross-check.

It happens in the US for worker's comp, but that's if you lose an arm. Pretty hard to fake that.

Mental health, "relatively easy" to fake esp if there's a lot of money waiting for you on the other-side if you get it right.