I can’t speak for other collectors but my focus is on ancient coins, mostly Roman imperials.
The amount of history and artistry in those coins is off the charts amazing, and every single one is like a tiny window into the past. To many outsiders it seems like one of the stuffiest things to do. It does require a good bit of research which can get a bit dry at times, but nothing beats that feeling of holding literal treasure of 2000+ years old.