It’s more about keeping the downloads code independent from the cache code. Once one depends on the other, you can’t change either one without considering the other. Minimizing dependencies is a way of reducing complexity.

That’s right, I was referring to the browser/client developer. The browser cache is treated as ephemeral storage so it’s not a safe assumption that a previously downloaded file is still there.

It’s simpler code to re-download the file than retrieve what cached version may or may not exist in memory or on disk. Developers often like to keep code simple at the expense of some kinds of efficiency, like this.

An image is usually small enough to be downloaded in no time on a fast connection, which is what developers usually have and don’t stop to think that others might not have.

A video is probably being streamed so earlier segments may no longer be present locally.

Spotify will force you to listen to an ad by pausing it if you mute the volume, then resuming it when you unmute.

I quit Spotify long ago so I don’t know if they still do it today, but they do have a way to force ads.