If a project you want to depend on isn't using a dependency management framework, how would you then make it work in your project? You will have to do extra work to define the transitive dependencies!

What needs to happen is standardization - this has been done in java because of it's maturity. There's almost no java project that isn't using the standard maven dependency management (even projects that don't use maven, such as gradle projects, would use maven dependency management, and export themselves as an artifact usable via maven).

Javascript has an even worse problem, so python isn't alone me thinks...

There are two main ways:

First of all, Poetry locks every dependency (even transitive ones) to the version you know works. This solves the problem of the project not using dependency management properly.

Secondly, setup.py allows you to specify your dependencies there, so most libraries use and specify that, which means that that isn't that much of a problem in Python. Sure, sometimes it is, but I haven't run into that particular problem very often.