Right, much more work for little gain for the developer. Then you have a bunch of developers all taking the easy way. And now all the system administrators run

Right, much more work for little gain for the developer. Then you have a bunch of developers all taking the easy way. And now all the system administrators running systems with those projects can't trust their packaging tools anymore, and have to do a lot more work in their daily workflow. Oh, and as a bonus, none of these systems have a secure update mechanism, so you've bypassed the inherent code whitelisting that comes with a system package manager with a centralised repository and a requirement for strong package signatures. At best, they do like PyPi and optionally allow a developer to specify a GPG key. So you have to do "pip install <bla>" and pray to the computer god that the developer of <bla> and all the developers of all its dependencies cared about code integrity and set up GPG keys. From experience, the chances of that are approximately 0%, because it's not a requirement.