Myst’s “inexplicable popularity”, along with games similar to it, was partially due to the advent of CD-ROMs becoming a viable medium for games. These games came out just before 3D graphics hit gaming. Myst was released at the same time as Doom. So these games existed in a time where CDs could hold much more data than disks, but most games were still 2D. So “pretty slideshow” games (along with FMVs) were a legitimate innovation at the time.