When a corporation sponsors the language, such as Java, Go, .Net, there's an inherent economic component which acts as a forcing function.
PHP being a foundation sounds nice. But consensus wasn't strong enough to affect the key outcomes.
making php is the core of (checks notes) php foundation
or is the management full of completely not technical people who use it to boost their CVs?
(Of course there's Log4shell, but that could've happened to a Rust-based stack too, and might be more likely to, considering the proliferation of deeply-nested dependency trees full of tiny libraries in that ecosystem.)
Several attributes make a safer ecosystem. An important one is diversity - technical diversity.
For an interpreted language, the runtime is important. Python has several runtimes, as does Ruby. Javascript also has several, from the few browsers, to node, deno and bun. PHP has for all practical purposes, only one. So if there's a security incident in PHP, it affects almost all users. But when e.g. JRuby has a vulnerability, it will affect only a fraction of the installed ruby applications.
For compiled languages, the tooling, libraries and runtimes is where diversity is important. With e.g. rust, the vast majority of CVEs come from libraries (crates). But since there often are several crates for a single concept, diversity helps mitigate here too.
I know you added a caveat and all, but no, PHP has a number of alternative runtimes just like the other languages you mentioned: https://github.com/gakowalski/alternative-interpreters#alter...
But again with all the ones you mentioned, they have a "core" runtime that the vast majority of production apps use, so if NodeJS has a vulnerability it would be just as big.
The interesting one will be whether "boring" ports - like recently Typescript's TSC from Typescript to Go and now to Rust - will be safer for being the same code and logic, converted to another "safer" language (by transpilers or LLMs).
Also, blameless post-mortems exist for a reason.