I don't know why I guess it was just cheaper and the A1200 was an entry Amiga. The 604 has double L1 cache and really outperformce the 603 but as they don't have L2-Cache on the Amiga cards they are a bit braked. A 604 at 233 MHz gives you up to 54% more power than the 603 at 200 Mhz.