He had personal reasons for that.

None too well pleased at the smiles with which his explanations of his bruised face were received, he made a sudden resolution to take a band of his own immediate neighbors and adherents and get on ahead of the Missourians.

He based his decision, as he announced it, on the necessity of a scouting party to locate grass and water.
Most of the men who joined him were single men, of the more restless sort.

There were no family wagons with them.

They declared their intention of traveling fast and light until they got among the buffalo.
This party left in advance of the main caravan, which had not yet completed the crossing of the Kaw.
"Roll out! Ro-o-o-ll out!" came the mournful command at last, once more down the line.
It fell on the ears of some who were unwilling to obey.