You could write an entire thesis on why memes have been so popular for so long. Indeed, multiple people probably have. Ultimately, though, all that the layman meme consumer needs to know is that looking at them makes them feel good, or at least it makes them feel numb to any of those big, bad feelings that we don't want to be reminded of.
Sometimes they even remind us of them, but do it in such a way that we can't even be mad. There are too many words and colors on the screen that are stimulating our minds for us to actually experience an emotion other than chilled. A collection of random memes is kind of a crapshoot of content, but it can still be relied upon to bring that pleasant numbing sensation. No matter what sort of day you've had or you're going to have, the effect of this list will stay the same.