First, a quote from the element set, as to what the coverage element is:
The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant.
And also a quote from the Miller text, page 114:
Use the DC Coverage element […] when an image depicts a particular place or time period, and when place or time period are likely to be important aspects by which users will want to search, browse, and retrieve sets of related digital resources[….]
As Dr. MacCall has noted, these are images of events. These events are taking place on certain days and times at certain places. I am not a huge football fan, but I believe that users will wants to narrow their searches by year/date and by the stadium/city in which the games are taking place.
Could other elements take up the slack? Well, the Date element could hold the game date, but it will be busy holding other dates, like date of file creation and date added to collection. And Subject could hold the place, but again, it will be busy with subjects like “Football” and “Football players.” Coverage provides a clean place to which software can direct a search to filter by time and place.
Side note: Is Coverage always necessary? Well, no. This image, for example, has no discernible time and place. It obviously has one, but it’s not a vital component of the image. This dachshund nursing kittens could be in Alabama or Wisconsin or Europe. It could be the 1930’s or the 1970’s or someone’s got their Instagram filters on. While the Coverage element could be possible for this image, it could also be absent without cost.