That's because it didn't need to provide more to make up for the slump in frequency, that was the whole purpose of the exercise.

The Honesdale Power Reserve can deliver up to 100 MW; 70 MW of those for 10 minutes and 30 MW up to 3 hours and it was built in less than 100 days.

https://en.wikipedia.org/wiki/Hornsdale_Wind_Farm#Hornsdale_...