What you meant is there are 10x as many rooms available on AirBnB than are one-bed places to let. That's very different from:
> There's 10x more rooms on AirBnB than there are long-term rents in Dublin;
AirBnB places would have high turnover, probably an order of magnitude higher than long term rentals. It makes perfect sense that more of the former would be vacant at any given time.