Why a licence is not a formality
A licence records that a person has demonstrated competence in a discipline and is accountable under a regulatory framework, usually with insurance attached to that specific work. When a task goes wrong, the licensing framework is what determines liability and what protects the building owner. A contractor performing licensed work without holding the licence removes that protection entirely, and it usually voids their own insurance for the claim.
That is why the exclusion holds even when the task looks trivial. Replacing a globe, resealing a basin, clearing a drain, treating mould on a wall or removing a pane of broken glass all fall under a licensed discipline somewhere, and none of them is safer because it is small. The building owner has more to lose from an unlicensed fix than from a short delay. Delay is inconvenient; an unlicensed repair that fails later is considerably worse.
