There are more regulations around employees than contractors here also, which often makes it not worthwhile for short term workers. Those regulations just mostly aren't around when you may terminate employment.

E.g. the entire I-9 thing and other IRS paperwork, who (if anyone) is responsible for various insurances (unemployment insurance, workers comp, liability insurance, etc), minimum wage and overtime for hourly employees, etc. Many things depend on this distinction.

I can't speak to differences from Europe as I am not familiar with that side of the Atlantic.