As an Indigenous person here in Canada, I can tell you that reserves here certainly were more restrictive in the recent past. One reason for this was something called the “pass system,” which forced Indigenous people to apply to leave a reserve. If their application was successful, they would be issued a pass by an Indian Agent (a government official on reserve) specifying a time they had to be back on reserve or face incarceration or forceful return to the reserve.

Reasons for the pass system revolve mostly around making it easier for Settlers to steal Indigenous lands without having to deal with Indigenous peoples, as well as crippling Indigenous rights to govern themselves and band together to oppose Canada. The article I attached, The Subjugation of the Plains Cree, discusses these points, and it also discusses the original intent behind the reserves, and how they were never meant to be what they are today.

It is also worth noting that many Plains Indigenous peoples became very successful farmers and ranchers after the over-hunting of the buffalo. This was to an extent that they were seen as being too competitive with Settler farmers. The pass system ensured that Indigenous peoples would be reliant on the Canadian State, and their success in farming and ranching was purposefully crippled to ensure Settler farmer success. Also, this enabled the State to continue using starvation as a technique to control Indigenous peoples. All of these points are also discussed by the article.

https://utpjournals.press/doi/10.3138/CHR-064-04-04

Hope this could help answer your question!