An engine having a diameter of 116 inches with a higher bypass ratio would easily be expected to top 80-90K lbs. thrust? 70K lbs. thrust seems kind of low for such a huge machine on A380??
already told you, larger fan size = larger bypass ratio as well as increased cold air volume with less work expended.
This means signficant enhancements in fuel efficiency and noise, which was the goal on the A380.
Sure, bigger fan output could be translated into more thrust, but it isn't necessary for this application, nor is the core designed for it. I think both engine's cores are designed to top out around 84,000 pounds with zero modification.
The GENX and Trent 1000 are expected to have 112-116 inch fans, too, to only generate a max of 72,000 pounds of thrust.