Games that are made specifically for solo play or is preferable for solo play has been on the rise for years. Most of them have been print and play though and usually not very well known except among the most avid solo player. Even more hard core than me. It's a niche within a niche.
When I say a game is preferable for solo play, I mean that the game is a multiplayer game, but that Board Game Geek has designated that the game is best played with just one player. So a game like One Deck Dungeon is made for 1-2 players, but the majority of players prefer bringing this game to the table alone. Another game that is a solo favorite is Mage Knight which can be played up to five players but solo is the preferred way to play. Unlike a game like Pandemic that can be played solo, but it is preferable to be played in a group of four players and so it doesn't count as a solo game.
There have been some published gems that the creator has made only for one player. The most recent game, Unbroken, received alot of buzz and had over 16,000 backers to the game's successful Kickstarter campaign which raised over half a million dollars in funding. Unbroken is solo only. So if a friend wants to join you, he or she can't and end up just sitting and reading a magazine while you play. It's a game where you were part of an adventuring party that ventured into a dungeon and was ambushed. Everyone but you were slaughtered. You were badly injured and you must prepare yourself with what little you can find to fight individual monsters that eventually will find you.
There also has been games that were released in recent years that are solo only games like Friday where you play Friday who helps Robinson Crusoe to survive hazards on the island. It is considered a classic for solo gamers.
There is a growing market for tabletop games for those that want to play solo only. I don't think it will surpass tabletop games for multiple players. However, people are busy and sometimes it is tough to gather friends for consistent game nights. So solo play has become an option to play a challenging game whenever you feel like it.
Then there is the announcement of the 7th Continent Classic Edition which is a solo preferred game that usually was only available through Kickstarter. Now it will be available in retail in the 4th quarter. It won't be as big as the Kickstarter Collector version, but it will be available for the masses. It is a solo or cooperative "choose-your-own-adventure" exploration board game.
Already there are many games that has solo variants rules like Terraforming Mars and there are games that create an opponent using an Automata like Scythe and Viticulture. But usually these games are meant for multi player and solo is just an option with changes to the rules. They are great games that want to appeal to solo players.
Already I see some solo only games that are coming up in Board Game Geek. One that I discovered is Blight Chronicles: Agent Decker which is a deck builder where you play an agent doing solo missions.
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Here is a list of solo only games
List of games preferable for solo play