It's the way data is organized in the GBA. It has to start with 08 to access the ROM data. 00 accesses the BIOS, 02 accesses the WRAM, 03 accesses the IRAM, 04 accesses the I/O, 05 accesses the temporary pallates, 06 accesses the VRAM, 07 accesses the OAM, and 08 accesses the ROM. Basically, just always add 08 to the beginning.