In recent years Apple switched from a big cat based naming convention for macOS to a Californian theme for their yearly software updates. That took them from nebula based backgrounds to scenic photography and it's been a nice change. macOS Mojave brings dynamic wallpapers that change throughout the day to reflect the current time of day. A nice touch in theory, it will be interesting to see how noticeable it actually is.
Despite being a Mac user for over 13 years now I've never really paid that much attention to the wallpapers beyond the system default and it looks like I've been missing out. With a phone it's different, you explore and personalise but how often do you spend looking at the background on your desktop?
The old Apple TVs have beautiful National Geographic screensavers while the new one has 4K fly over videos of various locations around the world and more are added every now and then.
When you look through the macOS offerings, macOS 9 and earlier were more abstract and gaudy. 10.0 bought more tasteful backgrounds but it wasn't until 10.4 Tiger that we saw anything other abstract shapes and 10.5 Leopard when we saw a real range of options. Not that abstract stuff is going away...
And there's some really fun stuff coming too: