The PyPA team has done a lot over the past five years. The changelog for pip (https://pip.pypa.io/en/stable/news/) contains quite a bit, PyPI was migrated to Warehouse, and there have been several PEPs focused on improving the packaging situation. A lot of these ideas come from various people in the community and get formalized as official recommendations or tools, but these things take time, especially accounting for backward compatibility in an ecosystem as large and mature as Python's.

The short answer to "why isn't this solved?" is "it's hard, and there's a lot to do". Development practices change over time, and the tooling continues to evolve with them. It's easy to see a broad survey like this and think that there's too much going on, but taken at a high level, the space is definitely trending in the right direction.

(Note: I'm not part of the PyPA, but I'm interested in this area and try to follow along from the outside.)