The Lunars probably have some tremendously perfidious uses for Truestone, so
they probably have some plans to obtain it. Outright force probably wouldn't
work; magical force probably wouldn't work; no doubt they're busy
Illuminating some poor Storm Khan (probably by corrupting a loved one
first). When he rejoins the camp at the Block, he'll gradually disrupt the
camp until the Lunars can make their move.
Who knows? Maybe the Lunars also WANT to free Wakboth.