Per https://developers.arcgis.com/net/latest/uwp/guide/geometries.htm, "The ArcGIS system supports both straight and curved segments, but at the current release, only straight LineSegments are supported in ArcGIS Runtime SDK. Multipart geometries can be composed from and decomposed into segments if required; until true curves are supported fully, using point-based methods offers equal functionality."
Not supporting curved segments in the SDK causes issues with functionality in mapping applications. Allowing these would cut processing times and simplify workflows.
See Case 02264264 for reference.