why it is that connection that is fused and not the ignition sensor?

Actually, both connections should be fused. I don't know whey they did not include a fuse block on the empeg harness there. Note that the car's radio-ignition-sensor-wire is almost always fused elsewhere, sometimes more than once.

Doesn't the fuse block on the yellow wire also contain a noise filter? Or am I remembering that wrong? Perhaps the reason it's there isn't so much for the fuse, but rather just to have the noise filter there.