Because it's a different type of DC-DC converter. 405/445 diodes want a much higher forward voltage than IR and red diodes do. 405/445, when running in a host that uses a single li-ion, or a pair of AA's, etc, will need 'boost' drivers. Meaning they RAISE the output voltage higher than the input. IR/660's will typically need 'buck' drivers. Meaning they LOWER the output voltage compared to the input. Mismatching your driver to your LD will result in three possible outcomes. A dead LD. A dead driver. Or both.