I assume the first screenshot belongs to iPhone 14 and the second screenshot belongs to iPhone 15 (dynamic Island). If my assumptions are right which wallpaper on iPhone 14 is not available on iPhone 15 is unclear to me.
I see that the iPhone 15 has an additional wallpaper collection which is not there on the iPhone 14.
This is what iPhone 12 Pro iOS 18.2 has. See the pic below.

Wallpaper options on an iPhone often evolve with major iOS updates as Apple introduces new designs to reflect the aesthetic and features of the latest software. These wallpapers can include dynamic, still, or live options that highlight new themes, color schemes, or technologies (like OLED displays).
Apple may choose to discontinue old wallpapers for various reasons, such as maintaining a modern look, aligning with updated branding, or encouraging users to adopt newer designs. Conversely, they may occasionally retain or reintroduce classic wallpapers for nostalgic value or by popular demand.
Users who prefer older wallpapers can sometimes find them through third-party apps or websites, although these may not offer the same quality or resolution as native options. For many, wallpapers are a personal expression, and their availability significantly enhances the customization experience.