en.wikipedia.org/wiki/Compact_Disc_Digital_Audio

The format has also been influential in the progression of video game music, used in mixed mode CD-ROMs, providing CD-quality audio popularized during the 1990s on hardware such as PlayStation, Sega Saturn and personal computers with 16-bit sound cards like the Sound Blaster 16.

In other words, the quality was similar to CDs because the technology was the same.