Why should they? For the same reasons as always. They still need workers in order to make more money.

If they -don't- need workers, they shouldn't be hiring no matter what the economy or government looks like.

Well, it's implied that we're talking about hiring more workers. For an established firm, there are many options:

Leave money on the table. We're all familiar with companies that have died from expanding beyond their long term prospects or a short term down turn.

Get more out of your current workers; plenty are willing to work overtime for the usual compensation (obviously I'm talking about non-exempt workers).

Hire part-timers and/or contract workers.