The A340-500 and -600, the 777-300ER are all fine aircraft, but they're too big for these missions. They can't sustain a LAX to Berlin or Stockholm route - they'd be half empty constantly.
And I have to disagree on the CRJ - it's the quietest aircraft I've ever flown in. I'd rather sit in that for 10hrs than stuck in the middle seat on a 747.
I recently did LAX to Cape Town, routing through Dubai. The LAX to Dubai bit is about 16,5hrs and then it's another 9hrs to CT. Just for fun I tracked it at 8700nm as a direct routing. That's on the very edge of what the 340-500 and 777-200ER can do. And certainly sucj aircraft would be even more unsuitable for such a skinny and extremly long route.
Time will tell. Maybe it's just not profitable, no matter what size, as someone said.