So now you have to fork it, come up with a new name, and then publish that instead. And then hope everyone who depended on the old package switches to your package.
Reddit had this same problem with abandoned subreddits. They instituted a policy where you could apply to take over an abandoned subreddit, so if there had been no mod activity you could take over.
Pip needs a process like that. They need a way to take over an inactive project. Safety would be a big concern, you don't want someone malicious taking over a popular but abandoned package and then hacking it. But safety the other way is important too.
There is also the odd situation where you could end up owning the code and not the package on pip. When my company acquired another, we got all their code. We only realized later that we didn't get the credentials for pip. Luckily the old owner was kind enough to just give us the credentials, but we could have been stuck owning the code but not the pip package.