It's not just a download manager!

Imagine a page with 50 links, that you each have to download by hand? Nope! Just DTA and a filter to choose what you want.

Photo gallery? Same!

Open a bunch of stuff in different tabs, and want to download the same thing (eg. .zip file) from each open tab... DTA all tabs, and *.zip filter.

Regex filter? Sure!

The basic download manager part is just an extra feature, that you usually don't need.

Still, one could reasonably expect that applying a functional pipeline to web page contents (extract and filter links, pipe them into the download queue) should be regular web browser functionality.

What's wrong with download managers?

Should I only use the one provided by my Web browser? Should I not download the content that I want to access locally or share between devices without being obliged to stream/download it again from a server?

There also some websites that throttle your download speed, you can fix that by using parallel download of same file.

Some countries and ISPs do this as well. Lots of uses for download managers

The thing is, a browser is already "managing" downloads. If browsers implemented their internal download management reasonably, people would mostly not need to bother with an extension.

Yes, they are still useful. Download managers can download specific range of files that we are only interested in which it can be filtered out. Like youtube-dl and gallery-dl, they are a specialized download manager and did amazing job with it.

If I find a gallery of images that I like to keep. I can use gallery-dl for that and use gallery-dl "instagram.com/boburnham" in the command line and it will crawl and download the images within the gallery.

Batch downloads are still useful.