Lots of games can be made by just starting to mess around and seeing what works. You get a guy on screen, have him jump on stuff, or shoot stuff. Or you put a city on screen, click on squares to build houses. And so on.
Such games are easy to find because they don't require a theory of what's going to work. You just try random simple things and see what feels good and chase that. It's not easy to do well, but it's a shallow process.
But as time goes on, such low-theory games are more and more oversaturated. The basic "objects bumping into each other" and "map painting" and "number goes up" designs are more and more already done.
To succeed in the future, designers will need to start having actual theories about what will work. They'll need to be able to posit a design that can't be built in a game jam, and why it works, and be correct, and then build that. There's a huge universe of games that can't be made by just trying simple verbs and seeing what feels good first try.
It means that in the future, design insight and analytical ability will become more and more essential in making a successful game. If everyone is doing basic and obvious designs, the differentiators are tech, art, writing, or marketing. In the new era, the differentiator will be whether you are able to find a great set of mechanics that nobody else can find.