I think the knife sheath, small footprints and campsite were found early on, while they were still searching the Kendall State Forest. I don't think they went that deep into the Middle Brother State Forest. By that stage, they were going along dirt roads within that forest and mainly looking along those roadsides, to see if anything had been discarded from a car.
I think they also stopped the search, because they'd been searching for ten days and that was deemed to surpass how long a three year old could be expected to be found alive. They had experts advising them on that.
They must have been receiving new bits of information throughout these ten days and, while I understand they were already pursuing other lines of inquiry concurrently, they decided to *focus* on pursuing literally hundreds of pieces of information they had received. Maybe they are hoping that after assessing all these bits of information, they might have a more strategic direction for further searches.