It's a nieche.
And it depends on what you think outdated means. VHS tape is outdated, deprecated and basically useless in current tech environment. But game genres, styles and mechanics do not become outdated. If old and superseded by more modern approaches they become "retro". Just look at pixel art. Outdated for decades, but still created.
https://itch.io/games/top-sellers/tag-text-based will give you data for comparison, since you ask about commercial success. Yes people are buying text games. But most of those are not pure text.
https://itch.io/games/top-rated/tag-text-based will give an inkling about popularity without considering payments.