One thing I've noticed hiring in both the USA, Australia, and Europe is the huge amount of 'hidden' taxes in Europe.
For example, if I hire a worker even on minimum wage, I'm paying up to half of their gross labour cost (depending on the country) as taxes to the Government! This is called things like a social security tax, healthcare tax, disability tax, etc etc.
By contrast in the USA you have one pretty simple and low payroll tax, plus health insurance. Australia has it even better, with no health insurance, though you do have mandatory superannuation/retirement fund contributions on behalf of the employee (all still much lower in Europe).
This creates huge incentives in Europe to just pay cash in hand, or say pay the annual bonus or overtime as cash. There are also a lot of companies afraid of growing larger and hiring more staff, because it will make their cash payments harder to conceal.
I hope from this boom in the US that the Federal Government can remove payroll taxes there. Combined with a move to a single-payer healthcare system, hiring and paying US employees could be the simplest on the planet.