Indeed, although Thanos had years of setup, it was
mostly short appearances, vaguely ominous lines (which in hindsight don't make any sense now) and the promise that he'll eventually square off with Earth's Mightiest Heroes, with his backstory mostly crammed into Infinity War.
The novelty is that this area unlike most others has at the moment an
appearance of moving in unison over a
short decadal time span with this
mostly external forcing.