This question has been plaguing me for the longest time, here's my take.
Garfield has been going on for a fucking ridiculous amount of time. At this point every interaction in the strip that could possibly occur has taken place, every possible gag involving the characters and even those that do not has occurred. At this point Garfield exists entirely off of a combination of nostalgia, comfort, tradition, and forces beyond our comprehension. Every strip in incredibly safe, Garfield himself has not changed in decades, the art style has not had a significant update in a long time, and the humor is based on you knowing the characters or completely lacking whatsoever in order to stay safe. Some of the strips have literally been, Garfield waking up, complaining, and then eating lasagna. And yet we laugh, because that's what we do. With all the rapid change in this universe somehow, Garfield defies the touch of time, transcends the only true constant in this reality, change. This repetition of the mundane framed in what we are all supposed to see as wacky humor has lead us to this shitposting you see now. Garfield is inseparable from humor, these posts simply see how far we can take it.
In summary, Garfield is everywhere but is also impossibly the same everywhere. He is culturally inseparable from the laughter that is so primordially ingrained in us, but at the same time has nothing to do with it as he is.
He is the sleeping paradox of human humor that we cannot even begin to describe, pray it never fully wakes.
I ATE THOSE FOOD