The goal of OSS is not to show off your skills as some elite programmer.
I think the quality/bugginess isn't as much of a factor as the fact that the codebase was not written with the intention of becoming OSS. Things like lack of documentation, hard-coded secrets, inflexible hosting/deployment, etc. are difficult to account for after the fact. And if you ignore these things and just "throw code over the wall", then virtually no one will even look at your code, let alone use it. Kind of a waste of time just to indulge a few self-righteous commenters on some message board, if you ask me.
A lot of OSS software was written with the intention of being open-sourced, so many of the things that make open-sourcing a previously-closed repo difficult are considered upfront.
What's the goal? You make it sound like I have an obligation to do it for some utilitarian reasons, while in reality maybe one or two previous customers would use it while migrating to something else. It's crap software with much better OSS alternatives already.
It either dies with me or dies as an abandoned repo I need to be ashamed of.
Reimplementation saps alot of productivity from the economy.