The really memorable memes will still pop up occasionally even after their main run, but people have short attention spans, so the joke is only funny for so long. That said, the lady yelling at cat meme has had a spectacularly good run.
OK boomers make older folks angry because the millennials do not listen but agree in a way to say "ok, but shut up". Sadly, millennials don't get they are at the bottom of the food chain but for companies that are willing to sell trash (nike, addidas, apple...)
Here's the weird thing about the OK Boomer phrase: It's making older folks angry but it's not even a real insult. It's just the equivalent of kids saying "yeah, whatever, old-timer." ...It's just mild ribbing yet it's legitimately getting folks huffy and upset.
I don't know, the 2 meme you pictured in this comic already got a life spam longer than months. Think Uganta Knucle was hot for about 3-5week, and OK boomer is still hot (+4 week?)