Valve can remove games from sale for any reason they like - it’s been a point of consumer contention when they are accused of censorship for certain risque anime games, too.

• They can completely remove a game from sale if it turns out to be bricking people’s computers or function terribly. (Sony did this with Cyberpunk on PSN, without CDPR’s approval)
• There may be suspicion the game is not legitimate for sale, for instance it illegally uses someone else’s work.
• Going country-specific, if a game is revealed to be slightly less than universally positive to the perfectly infallible, totally-not-genocidal Chinese Communist Party, they may want to stop sales in China.

If a game lets you buy it in Tanzania, download it in Tanzania, and then to play, has you sign an agreement that says “I truthfully state that I do not live in Tanzania”, then that bone-headed agreement reflects poorly on Valve, so they have almost a legal need to take it out of sale in that country.

Basically, each country has its own laws of sale. Having those switches to turn off sales in certain places is important for the store’s own safety. While 60% of the blame for selling a faulty product goes to the manufacturer, 40% still goes to the storefront that chose to stock and sell that faulty good. In this case, the fault was specific to the country of play.