Ignition switch circuit on bikes

[His Dudeness]

If you look on the wiring diagram for the Fazer and for most bikes from what I can see the main power wire runs from the battery, through the main fuse then to the ignition switch, then from the ignition switch to the fuse box and from the fuse box it runs to all the other circuits through the various fuses. That means the ignition switch and the connectors and wiring to it have to take the full switched current for the whole bike. If you have a fault on that circuit like the common burnt connector going to the ignition caused by a poor connection in the connector or high resistance in the ignition switch from old age and wear and tear, the voltage to everything drops including the ignition coils so you would have weaker spark. So the question is why do they design it like that where the ignition switches all the current? Would it not make more sense if the ignition switched a relay and the relay powered the fuse box? That way the ignition switch only passes a tiny current or is there a reason why they use the ignition switch to switch the current and they don't use a relay?