Here is why: Standard NES emulators (like FCEUX or Nestopia) were designed to read one game at a time. A multicart is a "custom mapper." The 852 In-1 uses a proprietary, often reverse-engineered mapper (usually , Mapper 52 , or a variant of UNL-KS7032 ).
The NES homebrew scene is thriving. Sites like Itch.io offer free, original NES games created by modern developers. Download Nebs 'n Debs , Micro Mages , or Alter Ego – these are new, fun, and legal. 852 In-1 Nes Rom Download