I speak in both cases. Retention of users in games F2P, for example, depends of constant content updates: new challenges, new characters, new updates, christmas event and that sort of thing.
It's like a website or youtube channel. When there is no novelty, the users go somewhere else better, among the many that exist.
And procedural generation is a way to generate this content. And make the game more variation, more uncertainty, more possibilities, more surprises, more new things to talk about. And without the need to stay always producing new content. And you can fill the time with something as important as this - and not only content.
Procedural generation with artificial intelligence is still more powerful. Because instead of creating random things, you create things based on data, about that users like, dislike, do more, want more.
Better than that is just the users themselves produce the content.
Because this is the way of Facebook, Twitter, Youtube, Minecraft, etc.
That are "virtual environments" with the best users retention rates.
This is why they worth billions.