This is confusing to me and seems somewhat arbitrary. Anecdotally, at any given time it seems that of the top “hot” or “trending” questions at least half will be about AI topics.
I’m picturing something like “This famous AI guy also happens to be a prominent Manifold user and has pulled a lot of his followers onto the platform”, which I think is why there are also a lot of questions about the streamer Destiny, far more than any other streamer.
A lot of the initial users came from LessWrong, which has a strong emphasis on AI and existential risk from AI.
LessWrong was started by Eliezer Yudkowsky who is The "AI Risk guy", and is an active user here.
I think the strong interest in AI from users on here comes from the fact that "prediction markets" (like Manifold & Metaculus) is a tool discussed in "Longtermism" circles. This includes discussion in making decisions about the long-term future of humanity such as how to handle existential threats, (super intelligent) AGI, etc.
A name that comes to mind is Robin Hanson who is a research associate at the Future of Humanity Institute of Oxford University.
On a personal note, I learned about Manifold only recently from the YouTube channel Rational Animations which talks a lot of the ideas I've heard from Longtermism. From what I've seen, the YouTube channel and Manifold user base appears to be very similar which I don't find surprising.
In short, AI is talked a lot here because people who have interes about prediction markets also tend to be at least familiar with Longtermism which tends to have a stronger interest in the future of AI than the general public.
The Rationality writings were primarily intended to help people understand Eliezer's arguments about the Singularity (source: Logan Bartlett interview, May 2023).
Truth-seeking is a primary goal of Rationality, and the idea of Manifold is closely related to truth-seeking (via temperance of bias, wisdom of crowds, courage to bet etc.).
Also, people interested in machine learning have mentioned Manifold on their shows (e.g. Lex Fridman).