The developer overlooked some nuances of Steam’s rules.
Recently the creator Tecopark accidentally made their project PICO PARK: Classic Edition permanently free on Steam. This was not part of their original plan.
The creator missed a specific Valve policy detail:
“I intended to switch to a paid distribution model after releasing the update with online support, but I forgot that once you move from paid to free you can’t go back to paid! :)”
PICO PARK: Classic Edition is a puzzle-platformer. The update added online play, refreshed visuals, and included various fixes.
Tecopark encouraged players who enjoyed the first game to explore the franchise’s other entries (those are paid).
Source: iXBT.games