Edit: I'm not necessarily disagreeing with you but I just want to know what your reasons would be to see it die rather than be improved.
Or indeed developing a successor. Loads of people bitch about how bad PHP is - I see very few efforts to even come up with a better alternative.
Instead of the developers growing and improving, and so pulling the entire community upwards, many simply choose to leave. I've had this personally with Drupal: many, many years did I poor a (joined!) effort into getting proper TDD, OOP, deployment strategies into this CMS, but in the end I gave up. I mean: why put effort into making Drupal something it does not want to be; while a few weeks of learning a new language, the thing I wanted Drupal to become, already exists.
I think PHP is mostly a station in the career of many webdeveloper, before they move on to what are often considered "more professional environments". Sure, there are a few brilliant and very professional PHP-devs who stick around. But relatively seen, they are a tiny minority.