I think the answer is in the question. Because they are new. They are an indication of "the good one was gone, so I settled for this". This is 2018, unless you are the Einstein of domain names, coming up a valuable hand-registered domain is the same as a scratch-and-win lotto ticket. BTW I assume you are talking about .com. The new G's have a better success rate with a name/value ratio because the TLDs themselves are new(ish), but the sell-through rate is unreliable.Why do newly registered domains retain less value?