Last year, Valve took action to mitigate the number of trading card farming games on Steam by developing a confidence metric that prevents games from dropping cards until it believes real people are really playing them. Now it's doing the same thing with achievement farming games.
In a brief message posted to the private developer group (which we can read via SteamDB and Reddit), Valve says that these achievement farming games aren't being used by many people, but that they confuse algorithms and users. Because of this, if a game hasn't reached the confidence metric Valve already developed for trading card farming games, it will be limited to 1,000 achievements, and those achievements won't count toward a player's global achievement count or be displayable on their profile. The game also won't count toward the number of games they own, and won't be eligible for coupons.
A notice is now displayed on the store page of any game that falls under these restrictions.
Running Through Russia 2, for instance, currently displays the message above. It is possible, though, that Steam's 'learning' will lead to the restrictions being lifted in time.
The original Running Through Russia is not restricted, though it appears that games which were released before the new policy took effect are exempt. USA 2020, which has a mode that simply awards the player achievements over time, is not currently restricted, either. We'll have to see going forward what it takes for the algorithm to decide that a game is 'real' enough for its achievements to count.
"We don't believe these constraints will negatively impact real games in any way," said Valve, "and the removal of fake games should improve the Store experience for everyone."