It was discovered by Reddit user 'thomasthe1st' on an r/Steam thread that hundreds of games were being removed on the Steam Store, and more seem to be following suit. The changes were noticed thanks to the use of a third-party Steam Store tool and mostly seemed to consist of low-quality, independent titles —essentially shovelware.
Alexandra Frock, developer at Anarkis Gaming, noted in a Twitter post that a large quantity of the removed games are associated with Dagestan Technology, a Russia-based publisher. The company operates under many names and is known to be guilty of abusing Steamworks tools.
Valve has since released a statement confirming that it is contacting publishers it knows to be misusing Steamworks tools and removing their games from the Steam Store. Dagestan Technology is among the targeted publishers, but Valve states that it isn't the only one.
Players have been calling for better curation on the Steam Store in recent years, with a growing onslaught of what is perceived as 'low-effort junk' arriving on the marketplace. It's too early to tell with any certainty what this story will lead to in the long run, but it could be the start of a more stringent approach to allowing products onto Steam on the part of Valve.