Here's why:
* Flash games are web-based games that use Adobe Flash Player. Pokemon Emerald is a console game originally released for the Game Boy Advance.
* Console games require a physical cartridge or disc to be played on a dedicated gaming console.
You might be thinking of online emulators that allow you to play older games like Pokemon Emerald on a computer. These emulators are not flash games, but programs that mimic the functionality of a console.