In Flickr’s case it’s because they were owned by Yahoo and basically mothballed for years because it wasn’t part of Yahoo’s core business.

After languishing without any changes for several years, they got bought by SmugMug a few years ago. SmugMug is a better steward than Yahoo was, but it’s hard to make significant changes to a product that’s essentially been in maintenance mode for a decade+ without access to the original programmers who actually knew how things worked.

Flickr is still useful, but I personally prefer Smugmug (who bought Flickr some years ago).

that thing where the entire scene is monochrome except one person in bright clothing

please learn to take good photos without the “look! this is the main subject! i am so clever!” cheat code

If you work on a desktop computer, consider using a photo folder to show as either your screensaver or desktop background. Windows (at least) can be set to shuffle through different backgrounds periodically.

You can also use your own photos as the background for a Chromecast if you want to see them on your TV.