The A380 is undeniably capable (and yes, very comfortable for passengers). But it is technically far behind the 787 and A350...when Airbus were investing in the A380, they basically built the best of the 'old' generation technology aircraft. Metal wing, part metal fuse (although the use of GLARE was an advance), and engines a generation behind the 787 or A350. Add to that, the wing was designed for the even bigger -900, so was somewhat compromised on the -800.
I think it was Richard Branson who said the aircraft could make a pile of money for the airlines, but nothing for Airbus...he wasn't far wrong. If you can fill it, then it makes money, but not enough people can fill it on enough routes...particularly when faced with the challenge of the modern twins, offering frequency over size.
BA are an interesting case in point...they seem keen on additional frames, but only at a different price point (even second-hand). Although the 777-9 order might herald the end of that idea.
Ultimately, it does seem as if the A380 was a vanity project. Boeing (when they were managed by people who knew) said the market wasn't big enough. They were right.