The companies with well-resourced dev teams would have been able to deal with it. But for every one of those there's 50 companies with no dev team who are sending frantic emails to the guy who quit 3 years ago asking if he's available for some urgent work. And another 50 that are not sending any emails because they're oblivious and will get pwned in a few months.
A lot of PHP apps are old, unmaintained or run by people with no idea. That's kinda it's niche.