The big carrot for ETOPS/EROPS was 180 minutes - with that you could go pretty much anywhere in the world (the most limiting case being US mainland to Hawaii), although the routing might not be optimum. At 210 minutes, few routes became sub-optimum. When you start talking above 300 minutes, it's basically a very small number of south pole polar routes - and becomes something of a 'mine's bigger than yours' exercise.
While overall shutdown rate clearly comes into play, a large part of the ETOPS equation is that most engine failures occur during takeoff/climb, not during cruise.
All that being said, those of us who put passenger comfort above price are clearly in the minority. If the average punter can save $100 suffering in a 777-10 instead of a relatively comfy A380 or 747-8i, they'll jump at the chance.
Boeing clearly recognizes that the future of the 747-8 is the freighter, not passenger. The 747-400 has proved to be hugely popular as a freighter - but most of the -400s are getting seriously long in the tooth (100k+ hour -400s are becoming the norm). Those 747-400s are not going to last forever, and Boeing is betting pretty serious money that eventually 747-8F are going to be needed as replacements.