They did. At least one artist said they didn't give permission for their assets to be used, but the developers grabbed from a few artists.
They even removed the patreon marks from images, and it looks like where it was easily possible they removed artist signatures.
Do not confuse people with your "right" opinion. All your complaints were answered in the discussions of the game.
All three artists gave permission. Art is not stolen. Do not lie. Otherwise, why indicate them in the page description and in the game itself? For fun?
Steam rules do not allow advertising of a Patreon links on artworks or in the game itself. This is the reason of blur.