I feel that many memes these days are somewhat manufactured. Quite a lot of people go out of there to find something "memeable", instead of letting something catch on naturally.
A lot of recent memes are just taking quotes from recent media that are ultimately unmemorable, which is why we forget them quickly. I've noticed more than a few are things taken from somewhat older media, which is more or less just people scouring media looking for something to make a meme, whereas for the majority of these, the fact that weren't memes already is usually an indicator that they are not worthy of being memes.
I recall back when Bill Wurtz's History of the World video came out, and someone complained that "The Sun is a Deadly Laser" was not worth making a meme out of, and that "You could make a religion out of this" was more worthy. This completely misses the point of what a meme is. You don't just decide to make a meme out of something, it's something that sticks with you, whether it's a moment from a video game, film, book or even comments and forum posts. "The Sun is a Deadly Laser" was more popular because it was a quick, catchy jingle that stuck with people.
TL;DR if you want to ignore my rambling: Basically what I'm saying is that people are going out of their way to make memes happen like they have some sort of quota to fill, instead of letting them happen, which results in a lot of either forced, unmemorable or just plain uninteresting things being labelled as "memes", when they do not fit the spirit of what a meme actually is.