It's the same reason Home Depot and Lowes carry essentially the same products at the same prices, even though there is an entire world of building materials they don't have. Despite vaulted "competition", large companies generally move in lock step. If they do something different they might end up falling behind the pack, and maintaining their position is the most important thing to do.

In this case, interest rates were lowered to basically zero and new money otherwise pushed into the economy, so the goal was more "growth" regardless of what independent analysis of the economy would say. This was the disconnect between Wall St and Main St widely that was recognized at the time. There was no way to know what the "new normal" would happen or what it would look like, so executives stayed with the pack.

And what really was the downside for hiring employees, even if they were just going to be let go later? Basically just the overhead of onboarding and getting them up to speed. And given that they were likely employed for a year or two, this wasn't even that wasteful.

Of course it sucks for the people whose lives are disrupted. But that's life in a paperclip maximizer driven by fickle centralized policy.