Anybody knows why there is gba slot in ds boxes?

I'm under the assumption that as long as you get a Nintendo DS game it will have that extra slot since the Nintendo DS

DS Insert a 3rd generation game into the GameBoy Advance cartridge slot and a 4th generation game into the DS card slot In the 4th generation game, you

ds with gameboy slot It works with Game Boy, Game Boy Color and Game Boy Advance games through its cartridge slot, while games from the Sega Game Gear

ds slot Find many great new & used options and get the best deals for Nintendo DS Lite Game Boy Advance GBA Slot 2 Cover Authentic