To put it very simply - Native American tribes were basically forgotten by the British during the Peace of Paris that ended the American Revolution. Since some tribes were against the colonists' fight for independence, Native Americans weren't seen as deserving in sharing in the rights listed in the Declaration of Independence that Americans fought for during the war. Some members of tribes in the north went to Canada while others in the west had to deal with the expansion of the American Frontier.

Britain did continue to support the tribes who fought against Americans on the frontier and that is one of the causes for the War of 1812.

Some great reads on the subject are:

Empire of the Summer Moon - S. C. Gwynne

The American Revolution in Indian Country - Colin Calloway

The Civil War of 1812 - Alan Taylor