Like, I know that Python is particularly prone to this, and if you have multiple languages needing C/C++ based libraries then I guess this is a concern.
But how many people have experienced this to an extent that containerisation seems like the right solution most of the time?
Making sure it's all correctly split into runtime, library, development, documentation, debug etc. parts, and ensuring that each part has the correct dependencies upon other packages in the system is a much more involved task. But it's this part that adds most of the value compared with simply building from source.
Making a "package" is easy. But the real point of packaging is integration with the wider system, and that part requires actual effort. Docker doesn't even attempt it. Docker is easy and convenient primarily because it pretends that problem doesn't even exist. It does the easy 10% of the job while ignoring the 90% of the work that takes the time and effort.
A “container” is an archive (eg, tarballs) of the contents, a hash chain of the construction, and some config data about cgroups and namespaces to run it with. Turn off the parts you don’t want — I usually turn off virtualized networking, for instance.
It’s a more lightweight package that doesn’t have versioning problems and doesn’t require crazy installation scripts — what benefit is traditional Debian packaging supposed to have?