Sunsoft answers the fan community
Meta Fight EX (Japan) and Blaster Master Enemy Below (U.S./Europe) were, in essence, direct ports of the Nintendo Entertainment System (NES) and Family Computer (Famicom) games which had launched the franchise. Many things were updated to help add value to the new games though. One such feature was a password feature to help people get through the difficult levels without starting at the beginning. There were also updated graphics, new introductory sequences, new storylines, and of course, new box and manual artwork.
The key factor of this game title's popularity? The gameplay. Sunsoft had maintained the gameplay while providing minor functional and cosmetic touch-ups to the rest of the engine (such as adding a password feature). With those changes and the re-introduction of Blaster Master to the GBC, Sunsoft had added another hit to their credit.