We're still missing big AAA titles. But there are hundreds (thousands?) of independent titles and fantastic games to choose from now. A lot of the change is surely due to the Unity game engine.

Many missing, sure, but at least we have started getting titles from the more known publishers and developers: Dirt Rally, Alien Isolation, Pillars of Eternity, Sid Meier's Civilization VI, Total War: WARHAMMER, Hitman, BioShock Infinite, XCOM 2, Deus Ex: Mankind Divided, Mad Max, Dying Light, Torment: Tides of Numenera, and Valve's own games.

As for numbers, there are 1950 Linux games on GOG and 6000+ on Steam.

Or maybe it says that multiplatform game engines have become popular.

True but the companies involved wouldn't have bothered porting to Linux if they didn't expect to see growth in that space. What's really interesting is that there are Linux ports for some of the SDKs. Really makes me question those who downplay Linux as serious platform for anything that isn't server related.

Good point; Unreal Engine has improved drastically in recent years and Unity adoption has been soaring. Whatever the cause, the consumer wins.