There is audio, just no sex noises . . . which, BTW, make a lot of games a lot less playable for me. Most of the time they don't even match with what animations show: slapping sounds at the wrong speed, cries that sound like orgasming when the MC's dick comes within a centimeter of a LIs vagina, etc. Sex sounds also tend to be way too repetitive, and you can tell the audio is looped and cut off badly. Usually they're just ridiculous.
And voice acting is usually pretty bad, too. Most who provide porn voices can't act to save themselves from a Jigsaw trap, but they get jobs anyway because there's no one else really. But I almost always hate the voices chosen. (Milky Touch was decent often, but some of those even weren't very good or even outright bad.) Please, no voice acting of any kind.
Unless someone does audio really well (extremely often not the case), I'd much rather have the audio be background music only (which Neko Paradise has). And, on top of all of the above, voice acting is expensive, especially for all of the lines of dialogue in a game. Something indie developers generally can hardly afford.