The answer is quite simple, actually. You are seeing a cross over of two different limits, set by two very different technical factors. You must observe the lower of the two limits, and you cannot perform the operation.
The weight limit for crosswind is set by the amount of anti-torque available from the tail rotor. As weight increases, the main rotor torque to hover in still air increases, and the tail rotor torque to trim the main rotor increases proportionately. This leaves less tail rotor torque for yaw maneuvering, so at some point, the crosswind capability drops below acceptable limits.
In the case in hand, regardless of the single engine performance margin (which sets the Cat A weight), the takeoff might look like this:
Pilot picks aircraft up with 30 knot cross wind. Pedals are within a few percent of the stops, but pilot doesn't notice (pedals would have about 10% margin at 17 knots). Pilot increases torque to initiate takeoff, and pedal goes to the stop but nose continues to rotate into the wind, passes through the wind and aircraft spins around in an "LTE" event. Pilot increases collective pitch instinctively to avoid ground, and spin rate increases (because anti-torque deficit is now much greater). Pilot loses cyclic orientation, brushes tail against ground, aircraft rolls over and flogs itself to pieces.
Any AH-1 pilots out there can testify to what these events look like, the Cobra is notorious for its lack of tail rotor power, especially in left quartering downwinds. The Snake has a chart that shows how poor the wind limits are with altitude and weight, down to less than 9 knots capability in some cases. The left pedal stop was my nemisis in 1000 hours of AH-1G flying in Vietnam.
Many helicopters have weight limits set by yaw margins instead of by engine power. The entire Bell line has tail rotors that are sized for sea level, and often become the limit with higher density altitudes. Note the performance charts for the 212 and 412 that mysteriously limit you to "wind within 45 degrees of the nose" while hovering.