On the contrary, they're more popular than ever. My most popular tools and games are all text-based.
As for why: great for beginning game devs; light on system resources; they appeal to readers and can take many different forms. Text-based games also provide superior accessibility if made with a little care. They can also be a breath of fresh air compared to the flashing images and frantic action of modern games. A lot of people need a break from life, not more of the same.