It's a venue thing.
I'm presuming with your reticence towards multiple rods that you only fish with one and if you're enjoying good success with numbers of fish, then that's fine.
Fishing a single rod on the venues that Paul, Warren, Murray and others target would lead to a year long blank.
Very large, mature, rich gravel pits, where bream go to the size that these people target are very hard venues with a small population of large fish.
3, 4 or 5 rods gives you the option to fish several areas using different baits and/or strategies.
If the venue was a type where the possiblity of 3 or even 2 rods were to go off at the same time, then Paul, being the responsible and caring angler that he is, would not be using a multiple set-up.