The trailer implies that these games offer worlds of boundless possibility, what it really is, is worlds with a bunch of generated primitives and sliders to change some numerical parameter. It's not that the trailers for these games lie, it's just we subconsciously expected more.
To achieve what we expect, the programmer needs to implement features that allow emergent gameplay and unpredictable situations to arise alongside procedurally generated settings. There are few single player games that actually pull this off. Dwarf Fortress, ARMA, and GTA V to name a few.
Yeah, sort of like those "32 in 1" and "112 tele-games" Atari cartridges, where each "game" was a permutation on the number of players, how the players were organized into "teams" combined with difficulty levels, or some such modifier. In reality, it was just the same game, and maybe you passed the controller around differently.
Or the cheap "pop station" handhelds that blatantly give you multiple copies of the same game, just with different "sprites": snowboarding, skiing, motorcycle racing, car racing, bike racing, etc all effectively identical.
Any programmer who codes needs to type. Just like any programmer who creates a game needs to design it. When I say the programmer needs to implement something I don't mention obvious processes like "game design" just like I don't mention typing. I also think a dedicated role of a game designer is not required in many games, especially indie ones.
Additionally, emergent gameplay, by it's nature of being emergent is not really designed. It's a sort of iterative process of implementing a feature and testing the consequences.
To achieve what we expect, the programmer needs to implement features that allow emergent gameplay and unpredictable situations to arise alongside procedurally generated settings. There are few single player games that actually pull this off. Dwarf Fortress, ARMA, and GTA V to name a few.