The reason it needs so many wires is this:

To avoid having to swap, the NEO4 (or its counterparts) has to pretend to be an acceptable boot disk. Then it can fool the PS2 prom logic into thinking that the off-phase laser scan to determine the type of CD has occurred, and it can set up all the other necessary conditions ready to continue loading from your import or backup. Thus the modchip needs to have access to all the necessary registers so that it can perform its functions. It also needs to control the DVD drive and so on. That means wires.