The word package is overloaded. There is a Debian package and there is a Python package.

If somebody wanted to package a modern Python application as Debian package they’d have to make a Debian package that contains several Python packages maybe as a venv or executable wheel, it is a solvable problem but a bit like comparing tic tac toe to 12d chess with supersymmetry in terms of the ambition of Linux distros if not the difficulty.

If you installed python packages as debs without any isolation you'd never be able to install two applications that depended on different versions of the same Python package.

The best thing about Java is that it is so xenophobic that nobody expects to have a working Java runtime installed with the OS so you never have to deal with a broken runtime installed with the OS. JAR files are remarkably self-sufficient so "write once one anywhere" is way closer to the truth than it is on "DLL Hell" platforms like Windows and Linux.

It takes more work to create and push a Debian package. Yes. But once it's done, it's DONE, and you never talk about it again. This whole article and thread can disappear, which is a MASSIVE time savings. The "DLL hell" you're referring ot exist on platforms that don't have package management, which notably does not apply to Linux, in general.

The funny part about Java is that "Enterprise Java" used to depend a lot more on things being in the base application server, and because that was, as usual, complete hell, it now went the complete other way and microservices will often "just bundle the entire application server" in the uberjar as a result.