Depending on where the area to be cloned is in relation to the background and what detail is available to use, and how detailed that area is can all affect the sharpness. Some imagejust work better than others depending on their content. Content aware is just the first starting tool, often you need to use the clone stamp or other tools to refine the area.
PS 21.1.3 on an iMac running 10.15.4. I think it's related to the image being half in focus and half blurry. When I select an area just to the left of the grass it fills correctly.