Because that would weaken the small settlement even more.
Explanation:
Sachem is the term used by Northeastern Native American tribes to refer to its supreme leader. The Sachem had to lead the tribe, solve the problems and protect those who were subordinate to it. The Sachems were very concerned about the desertion in small villages, because these villages were already weakened by their small size and the desertion would weaken much more because it could lose some warrior to the enemy.
The deserter would know the tactics and weaknesses of the village, so if defections occurred, more serious problems could arise.
<u><em>A sachem is the chief or leader of a tribe, and having anyone of your community do an act of defection (change loyalty to the opposite side) is the beginning of lots of issues, those including: treason, increasing number of deserters, a weakening tribe, etc. Those are the reasons why a sachem should be concern about defection.</em></u>
