As a kid I thought this was just a weird hotel thing. Got the backstory eventually.
TL;DR: ice became commonplace around the time motel chains spread across the US.
Ice was once an exotic import only nice hotels could offer. Its perceived luxury remained decades after refrigeration allowed manufacture. Hotels could still charge for it, so they did, but in the ‘50s and ‘60s ice went from cheap to essentially free.
Concurrently, roadside motor-hotel (motel) chains spread across the US. Among these, “Holiday Inn” was the first to offer ice as a complementary amenity. Competitors followed suit. National roll-out at every motel franchise happened quickly. Soon nearly every hotel offered self-serve ice as a standard amenity.
Nice history. Ice is awesome, what kind of psycopath's want warm drinks? Even if ice hadn't been some exotic luxury in the past, I would still demand ice.