Because companies earn money by producing goods or providing services, but those goods and services are required by burned out people.
Let's say your company can build and ship a product in 2 years and none of the workers end up crunching. What if every single client is not in the position to wait 2 years (because they are themselves crunching) so they go with the company that builds it in 6 months?
Let's say your company can build and ship a product in 2 years and none of the workers end up crunching. What if every single client is not in the position to wait 2 years (because they are themselves crunching) so they go with the company that builds it in 6 months?