Agreed, the GetRates API (and Rate Calculator in the UI) need to include SurePost rates.
They will never do it, this has been a reoccurring request for the better part of a decade. Way before this request was made in 2018.
Bump , Please add this feature!
You can use Shipping Plus app (www.shippingplus.co) for ShipStation to automatically have smart post selected when it’s the cheapest option