And how do you know they didn't quit?
The TTC, or any organization, would have a very tough time retaining top talent in those working conditions. It would't take very much for the best and brightest of their employees to find employment elsewhere. The TTC can find someone to replace them, but the quality of that employee certainly wouldn't be as good as the one they're replacing. Treating employees like this is exactly how once great companies lose their greatest talent, ultimately leading to poorer performance for the company in general.
A lot of firms private sector go to extraordinary lengths to accommodate their employees because of this.