Players differ substantially in how much they enjoy the learning process of a game. I've seen numerous people stay at the same difficulty level for years, just as likely to win or die to the AI after 3 years as they were after 2-4 months. That's not something where you just play more and suddenly you can beat deity. There are people who adapted to at least win on deity within a week. You have to actually change something about how you approach/play the game to improve. Not everyone cares whether they improve, which is fine. What's perplexing is when someone is frustrated that they struggle, but then still don't adjust.