A "lightly used" ship available NOW, which can be used to generate revenue, is probably a smarter investment than putting that money into a new build. The latter will not generate cashflow until it's launched...and with delays, who knows when that will be?
Also, demand for cruising is high now. Who knows what it will be down the road? Make some money on your investment now.
Assuming of course, that you can find crew to staff it! So yeah, I'm not surprised that a quality used ship would be kind of a hot commodity now. No wonder there's a bidding war.