I've done something like this for a couple of years, albeit not full-time. The project was written in Symfony 1.x and got stuck there, as Symfony moved on to higher versions and wasn't backwards compatible with 1.x. The codebase consisted of thousands of lines of poorly documented and commented code, intermingled with custom JS modules that nobody understood. When management wanted to implement changes, it would take days to comprehend the potential effects on different parts before I could initiate any modifications. The project would have required a complete rewrite, but the management was staunchly against it. This has been the most frustrating and unsatisfying tech work I've ever undertaken, alongside past tasks of migrating MS Access apps.

I sometimes find myself pondering why I didn't cease working on it, especially given the compensation wasn't particularly impressive. It's crucial to recognize and act when you sense that a project is no longer benefiting you, and simply move on.