We have respected the theme, it's not obvious though, because it wasn't our focus to get the narrative into the game first. First is gameplay. The narrative is, Hank is a flat earther. He has set out to demonstrate that the Earth is not spherical, by digging a hole. His theory is, if he can't get to the other side, the Earth is obviously not a sphere. But the game is endless. So the game is a liar.
Many people have interpreted the theme to make character in it lie, which is missing it. Others have made the game annoying. That's missing it too, in my view. Very few have done something clever with the theme. Here is one:
https://charu12.itch.io/mindless-runner
Not sure where you're going with the second bit of your discussion. I think it's a counter to my use of the word fun. I may have used it, but I did mean "entertain". At best, as you mention, they can be a learning vehicle. Ultimately, they are not a productive endeavour to consume, like films or anything like that. Hence, they are entertainment. If, however, they end up being annoying, the chunk of the market that enjoys them shrinks considerably, to the point that only clinical masochists can enjoy them, and they also have a taste, so it's not going to be 100% of that minuscule slice of the population. A better term could be "engagement". I certainly didn't experience that while playing yours. I experienced the game doing everything in its power to get me to stop playing.
Tomorrow I have to write to the organising team (on their request) a case as to why I think this theme was poor for the learning audience here. Your very rationale will be useful ammunition, specifically: "I did A to fit the theme". If the theme produces so many failures, there is a problem. So that should be fun. :)
Cheers.