The tracker is even better imo

For example https://tracker.debian.org/pkg/curl

It seems to put lore focus on the extracted dpkg. So you can browse and download the unpacked files.

I prefer the search on the original sites, but this looks neat if you want the payload of a package.

In that case, what's wrong with https://sources.debian.org (other than people apparently not being aware of it)?

sources.debian.org has the source for the package. apt-browse.org has the files that are installed by the package.

Compare:

https://sources.debian.org/src/htop/2.0.2-1/

https://www.apt-browse.org/browse/debian/stretch/main/amd64/...

You can see the contents of a package in Debian's package site, you have to go to the available architectures of a package and select the list of files for the one you want

You can also search contents of packages if you select the option in search (the other options are package name, description)

Also apt-file so you don't have to leave the terminal

For one, packages.ubuntu.com throws errors or is down all the time. (I got an Internal Server Error just now).

The usability of searching "package directories" vs "the contents of packages", having to toggle between package names vs "source package names" vs descriptions, and choosing substring matching modes is... well, very typically Linux.