You cant just point your finger at Sturgis and read a chart from a website to totally understand what is going on in South Dakota.
I have alot of connections in South Dakota and its complicated. For a long time many counties, up until July even, had pretty low numbers but over time, eventually, the disease came in. Sources include out of town visitors in general not just for Sturgis (South Dakota is big on summer tourism), residents travelling, residents getting tired of restrictions, etc… When I went up there over the 4th they only had restrictions tight around the nursing homes. Many businesses didnt even require masks. The disease mostly connected to a meat packing plant in Sioux Falls.
So basically you can NOT just point to the Sturgis Rally and go “SEE, SEE, look how that event caused all more cases in the state”. The two do NOT go together. The state was due for an increase and they got it.
Sidenote: the reservations who have a large population of vulnerable people, are doing a pretty good job controlling it with some even using roadblocks.