I agree. I love them. I'm lucky enough to have only flown in business and first on them (not because that's where I usually sit, comrades) on Qatar and Malaysia. They are lovely and quiet, especially upstairs. The Qatar ones are spotless, with a separate bar if you're in the posh cabins. Malaysia's are in poor condition as they can't make the sums work. KL isn't a big destination and there is a lot of competition for those wanting to change planes in that part of the world. They only fly the A380 to Heathrow and often struggle to fill them - the price I got first class for when I used it last year was not a huge amount more than economy on some airlines. Even this isn't going to last long, as they're replacing them with the A350 on this route and are reconfiguring some of their A380s to all-economy with tightly-packed seats, to be used for the Hajj and not much else.
The big downside with them, and a lot of the newer planes is the fact that they are so quiet. Without the droning of the engines like you get on the 747 for example, you hear everything so it's harder to sleep.
They do make sense for a lot of routes, particularly those where you are going to have to change planes in the middle of nowhere, like the Middle East. But for most airlines if it's the choice of two A350s or two B787s per day on a route or one A380 they will prefer the former as it provides more choice and the potential for shorter connections. Airlines don't want people sitting around airports either.