Why did riel return to manitoba?

That's a common mix-up, mate. He didn't actually return to Manitoba. A Métis delegation from Saskatchewan asked him to come back from the US. They desperately needed a leader to fight for their land rights and other grievances against the Canadian government. Their petitions were being ignored, and they were getting desperate. Riel felt it was his duty to return and help them, which led to the North-West Resistance in what's now Saskatchewan.