A bit more charitably: sometimes you might want to open up a DEB file and poke around in it in a system which is not Debian-based. AUR package authors do this o

A bit more charitably: sometimes you might want to open up a DEB file and poke around in it in a system which is not Debian-based. AUR package authors do this on Arch, for example, as do the maintainers of the Nixpkgs entries for some proprietary software which is only distributed upstream as DEB files. So the Linux desktop ecosystem as a whole doesn't necessarily know ahead of time which way you want to use a DEB file. Of course, an archive manager which can detect whether you're on a Debian-based system or not, and appropriately choose whether or not to show you an 'install' button after opening the archive, is very much possible and would be quite nice.