That's only because they are only "similar" on the surface. It feels like saying "football, volleyball and basketball are similar" just because they are all team games played with a ball.
If you are curious, vndb has a guideline you can see about what can be added here: https://vndb.org/d2
But only people who are really into computers read them, so they like to use game terminology to talk about them.
(also, none of the creators of "VNs" call them "VNs".)
By the 2010s many JRPGs such as the Hyperdimension Neptunia series and Danganronpa pretty much stole all the visual elements of visual novels and mashed them up with gameplay from other genres.
Phoenix Wright is the only one of those Westerners really know about.