image boards are just a natural evolution of the text board format. Even then, 4cuck is basically the only popular image board (still around at least, 8chan is basically a walking corpse now)

Text boards are just a part of the old internet. One that will die out, eventually. The image board too may die out one day, even among younger generations not as many people use 4chan compared to instagram, tiktok or even twitter. Twitter especially is not too dissimilar to an image board when you think about it, just far more streamlined and with accounts to show people how popular you are.

I think human psychology is the second reason. It's much more rewarding to get 20 upvotes on reddit, or 20 likes on twitter, compared to a text board which is not too dissimilar to an anonymous forum. The reason Reddit won out over most other forums is its upvote feature. Text boards rarely net you lots of (you)'s unless you troll.