Excerpt from this article:
If you’ve spent much time on the internet, you’ve seen a meme like the ones above: a picture, white words, a black outline, and the same exact font… Why do so many memes have the same appearance?
The answer tells us something about design, business, and how technology can help something stupid find traction… But by this point, the meme font has itself become a meme — a viral idea that’s very difficult to suppress. We expect memes to look a certain way, and that way includes Impact. The font is as legible as ever, and it resists user error, too (if somebody forgets the outline, adds a weird shadow, or even screws up the color, it will still look like a “proper” meme).