But bulbs aren't usually on when the property is empty for a week...And thats a common cause, bulb blows, householder replaces, circuit back on.
Whereas power circuit trips, cause unknown, owner shrugs shoulders, repair time variable.
Thats fine, still often reset / resettable quicker than a power circuit trup.
And fixed circuits mean few changes, more stability. No car boot battery chargers being added to circuit
and causing random trips.