Cetti's Warbler - WWT Caerlaverock

Terrific news from WWT that the bird is out & loud around the Sir Peter Scott Trail at the moment. However, it's apparently been present & shouting out for a couple of weeks! How has the bird not been heard by a visitor in the last couple & I'm struggling to understand why the birds presence on the reserve at least (no need to be specific), hasn't been announced until a time it can no longer be avoided? That's how it looks & I don't see the logic of it at all (if that's what it is?), sorry. So, Shannon Clifford hasn't got the second record for D&G, at all. PJ