It is actually quite ingenious.
The artist knows they are not going to make money off of the songs, so why waste money marketing the project before it's released?
Think about it. While the artist is developing the project in stealth mode, they can spend more time, energy, and focus on the project without all the expectations and distractions. Creating higher quality content.
Then when it gets released, the artist's core fan base decides organically what is good, and then they start promoting the project for the artist. The artist then makes a video based on the feedback that they get from the fans while it is still relatively new, and then starts drumming up interest for the project to the rest of the market.
The artist goes on tour, and makes the same amount of money or more, without all the unnecessary costs and headaches.
It's better than investing lots of money on a perceived hit, only for it to turn into a flop.
@Sakurabaism