Why is my aerial screensaver only 3 images. A beach, jelly fish and one other?

The Aerials screen saver clips are cache files that can be deleted at any time when the device needs the storage for actual content, even preemptively. The Aerials will be deleted when you select a non-Aerials screen saver type. The Aerials will download one new clip in the interval as you have set in Settings. The number of Aerials that you can download depends on how much storage is available on your Apple TV. To manage storage on your Apple TV, go to Settings﹥General﹥Manage Storage.

Aerial screen savers on your Apple TV - Apple Support

The Aerials are send randomized from a collection of close to 90 now. With the current version tvOS you can’t select which ones you want, but the upcoming version tvOS is expected to allow themes selection (cityscape, landscape, earth from space, underwater) for the Aerial screen savers.

You can set the frequency of when to fetch a new clip: never|daily|weekly|monthly. You can’t set it to fetch more than one at a time.

all I want are the cities back like I had before

That is not how it works. 🤷🏻‍♂️