I've never understood how you can get an erection or ejaculate just from text.
To add to some of the other reasons people have posted, K-12 I was that kid in school who was reading a new book every couple of days. Its pretty easy for me to visualize stimulating scenes in my head from just text. I have a lot of experience from all the reading.
Additionally, I'm asexual. I still have a libido and masturbate, but I'm just not attracted to the physical human body. Often times, the physical human body just repulses me. I need it to be text-only, be highly anime-ized, a deeper emotional connection to the person/character, or a combination of these to get off to it.
To say nothing of the development advantages. In other games, the visual assets are barriers to entry for content. For example, other games need to make graphical assets for each body type, boob size, dick size, hairstyle, piece of clothing, etc. And the extra code to load in those assets, have them be called up correctly, and render correctly.
In a text-only game, you can just shove whatever options you can think of in there and just need to code a variable descriptor that lets the game say "The ass is fat" in more than one way to keep descriptions from being repetitive.
Its significantly less resource/time-consuming. So, if you can get off to text-only, text-only games are able to attribute those freed up resources/time to other things. Enhancing the game in ways graphical games will often lack. (If time-management is good, anyway. Which sadly isn't the case for New Life's development.)