Those games are played by a demographic that only plays that game, or close enough. They’d consider themselves a Dota player before they consider themselves a video game player in general. These games aren’t played exclusively by that type of person, but a large part of their audience is the type of player who just plays that game. I’m having trouble digging it up, but the person who created Steamspy a number of years ago, before privacy laws made public profiles opt-in and interfered with its ability to collect data, found that the majority of Steam accounts only had a single game in their libraries.
GTA V is second only to Minecraft in copies sold across all of video games, and it still appears in the top 10 for copies sold on most months, 11 years after its initial release. It’s also available on other stores and consoles, so Steam is not a complete picture.