My guess would be that ads are incompatible with white noise use cases. If the white noise “podcast” inserted ads, I would guess that people would find a different place to get white noise.
"Moore and his white noise team... offer a subscription plan. But most people listen to the free, ad-supported version. Because Moore doesn’t want to interrupt the calming aura of his show, he opts to include only pre-roll ads."
"Reed, who is something of a white noise purist, knows he could make good money with advertisements. But he doesn’t include them because he worries the sound of commerce would disturb his audience’s restful slumber.
'It’s embarrassing to say how much money I would be making,' he said."