Turbulence intensity applies to the air around the aircraft.
The sustained load factor applies to the aircraft itself.
These are apples and oranges, one cannot be directly compared to the other.
In a simple model of a high-G turn, the air remains stationary, and the aircraft increases its lift N times. Thus its wings have to be designed to carry a load of N*W (with fatigue and safety factors).
Gusts or turbulence also produce forces on the wing. But not as much force as would be required to impart the same amount of acceleration to the aircraft as the apparent acceleration of air in the gust. A fan that blows at X fps doesn't make every object in the room move at X fps.
A gust of 90 fps across a stationary flat plate would impart about 12 lb/sqft of pressure. A modern airliner's wing loading is between 100 and 140 lb/sqft. Real numbers will differ a lot, because it's not a static case at all, and manifests as an AoA change, with increased/decreased lift.
Still, it's not extra G's of force, as that would require far more velocity.
What makes turbulence dangerous and very perceptible is the rate of change in acceleration, called jerk, not absolute acceleration. Its erratic behavior also contributes to vibration and fatigue. The added force is only a fraction of what the wing normally carries, but its rapid onset and cycling can be dangerous.
Increased design turbulence intensity is a requirement to account for these secondary factors, not to build more static strength into the design.