I'm afraid France Télécom didn't just give their employees "nothing to do", they actively made their employees' work life hell and harassed them psychologically, resulting in 35 suicides.

https://fr.wikipedia.org/wiki/Affaire_France_Télécom (this article is written rather poorly but the referenced newspaper articles explain it quite well)

Apparently it's a thing in Japanese companies for the so called "salarymen". Because the general expectation around these jobs is that they are for life, it's frowned upon to let someone go - instead, you will be sent to the corporation's rural office, with literally nothing to do 8 hours a day. It's designed as both a form of punishment and as a way to make someone quit.

For anyone interested in reading more, it's called the Boredom/banishment room

https://en.m.wikipedia.org/wiki/Banishment_room

A stupid question maybe, but if they are paid full salary for doing nothing why can't they use corporate time to work on something else so they get 2 salaries?

It's almost certainly against contract and would give the company justification for firing them.

When I read that I end up thinking that labor laws end up having unintended consequences. If you make it impossible to fire people, they end up being abused (I don't think that's ok, but it's absurd that we could connive a legal structure to somehow make unwanted employees appreciated).

So, constructive dismissal.