There was also the factor of many family groups in the immediate vicinity making the tactic of breaking contact and running not viable. The village couldn't be moved when attack was imminent so the only alternative was to fight like he11 and try and run over the army with weight of numbers which they did.
Yup. In Custer’s defense, he got some really bad numbers from his scouts. He thought he faced hundreds of Lakota, when in reality he faced them plus thousands of Sioux.