Keep in mind the A380 is a larger aircraft that can carry more people than the 747-8, which may explain some of the heavier weight. In a 3 class configuration, the A380 can seat 525 passengers, while the 747-8 in a 3 class configuration can carry 468 passengers.
When comparing Boeing and Airbus aircraft of similar size, the weights are roughly equivalent.
As for the 747... considering that it was originally designed in the mid 1960's, it has held up quite well. But, it's days are clearly numbered.
One reason that the 747 (and A340) are headed for obsolescence and A380 sales are flat, is the cost efficient large twin engine airliners, like the 777, 787, A330, and A350.
To establish a perspective, consider that the A380 program began around 1990. At that time, the big wide body twins weren't in operation, and the general consensus in the aircraft industry was that large airliners had four engines. The first wide body twin, the Boeing 777, entered service in 1995, and its operating efficiency wasn't really seen until the late 1990's, when A380 development was well under way.
Also, ETOPS certification had only been issued to twin engine airliners in 1988, (the A320 being one of the first to get the certification) meaning they were now certified for long distance over ocean flights. The changes that brought on (among many others, the demise of the triple wide bodies like the MD11 and L1011, whose third engine was added only to get over ocean certification) weren't obvious in 1990.
In the interim, the wide body twins have proven to be extremely cost efficient... to the point where one can operate two 787's for slightly less than one A380, while carrying the same number of passengers and having increased flexibility. In operation, the A380 needs to be nearly full to turn a profit... so being able to use two big twins instead gives the airline the option to simply drop one flight if passenger load is light, and save a bundle. Another advantage is being able to fly smaller groups of people directly to smaller airports, while the huge size of the A380 tends to confine it to major hub airports.
One bet that Airbus made with the A380, being able to move a large number of people with a single berth and single takeoff/landing cycle at a major hub airport to alleviate airport overcrowding (with aircraft, not people), hasn't panned out.
I suspect a bit of hubris might have played a role, however minor. Airbus had lived in the shadow of the giant 747 for decades. Building something larger probably involved some pride. Not a major factor, but pride in having the largest might have made the profitability forecasts appear a bit rosier than they actually were. Yes, the aircraft industry is definitely male dominated.
Is Boeing more astute? Not all of their decisions have worked out. They (and the US government) spent a fortune on the 2707 supersonic transport, before abandoning it. It is likely that Boeing will take a 1 billion dollar write-off on the 747-8 due to poor sales (only 51 were delivered for passenger service), though that pales in comparison to the 25 billion Airbus spent (and probably will never recover) on the A380. Boeing ditched the 757, not long before that size aircraft became very popular (the A320 filled the need, and picked up a lot of sales). Their performance in the Joint Strike Fighter competition in 2000 (that produced the F35) wasn't so good, the delta wing design proved unsuitable for carrier operations. And, the airliner Boeing proposed when the A380 was announced, the beautiful Sonic Cruiser with it's high speed (Mach .98), was stillborn when airlines expressed a preference for lower operating cost over higher speed.
This article suggests that the Sonic Cruiser might have simply been a red herring... not sure how accurate that is, but it does make for interesting reading.
It is unfortunate for Airbus that the big twin airliner put the four engine airliner in general on the road to obsolescence, after they had invested a fortune in the development of the A380.
But, absent hindsight, that may not have been obvious in the early 1990's.