It’s technically not escrow as that requires an independent third party. And it’s also not just for repair. It’s mostly an incentive structure to foster loyal and stable nodes. It doesn’t fully cover repair costs to begin with.
Does it matter that much why the amount is held back? I can imagine that including the explanation in the naming could help clarify, but it will also lead to more followup questions. Also check out this topic: So what am I missing regarding held back fees!