In what way is writing text on GIFs a meme? It's not even on the GIF, it's above. If you want to caption an (animated) image for social media, please just use normal text comments. They are way more accessible.
Well, putting the text in the image file itself makes the text+image combo easily portable between services. It lowers the barrier for others to share the content, with their own techno-tribes.
I guess this why the 'meme' form is so prevalent, today.