As Mr. Budge alludes to, the refrigerant gas can leak out over time. Most fridges I've seen have provision for being evacuated and recharged, just like car AC.
Problem is, if there's a leak and it's not fixed, the recharge is only temporary. Good luck finding a tech who can do it right, assuming he can even get the parts.
I have a small bar fridge my father bought over 50 years ago still chugging merrily along, and a friend who's into old stuff has one from the late '40s that's never needed work either.
They sure don't make stuff like they used to (shouted at the clouds).