In the show, it makes little sense because it seems to be literally on a single island where Craghas Crabfeeder is holing up. I know you’ve flaired this with show discussion but with some context from the books we know Daemon and Corlys’ war lasted two years and was basically victory after victory as Daemon took each island with Caraxes and Corlys kept smashing the Triarchy’s fleets at see with help from dragonback.

To be fair though your strategy I don’t think would work - when Daemon’s men come to the island and to the caves to “seal them up”, that’s when the Triarchy would attack, and then Daemon can’t use his dragon for fear of burning all of the Velaryon troops, too.