The increase in the number of scouts was actually not entirely targeted at Jiang Yi and company.
There were twenty-seven Demon-Killing Pearls in total. The majority of these would land in the Heaven Domain, a minority in the Chaos Sea, and one or two that would occasionally be found in the Earth Domain.
Every time these pearls were discovered, a conflict would ensue to gain possession over them. Ultimately, most of them would end up in the hands of the great family clans. Since the great family clans' young masters and young mistresses had these pearls, they naturally knew the location of the Demon-Killing Palace's appearance and would head there in advance… to stop the others who had the Demon-Killing Pearls.