>>42763312It was one of the first RPGs geared specifically at children. In fact, the genre of child-friendly RPG is very sparse even to this day. The fact that it was geared at kids also drew in adults who were scared of the "difficult" world of JRPGs.
As an added bonus: the competitive aspect further differentiated it from other JRPGs of the era. How many non-monster JRPGs let you battle other players...?
Mix it with the aggressive marketing and it took off hard.
What kept it going?
Nostalgia. College kids with limited time looking for something they are comfy with in a changing world as well as an excuse to socialize. Female trainers get popular fast in college settings,drawn in by cute critters. Male trainers are drawn in by waifumon and cute female trainers.
The trainers continue to nostalgia as they age. As adults they miss the "carefree" days of college and school. They decide to check back in on that game series they loved. It's still going. They buy it for their kids, using the kids as an excuse.
...the cycle continues...