1. PHP is very welcoming to beginners. That's of course a good thing, but the downside is that it's actually quite difficult to get quality answers on StackOverflow, which is rife with clueless trial-and-error answers and "Just use <completely unrelated heavy framework>, dude" kind of responses
2. PHP started out as a simplistic server-side templating/expression language; which is fine by itself, but without any kind of injection prevention is incredibly naive, and the reason for so many DDOS botnets. Of course, using embedded PHP (eg. in a processing instruction in your otherwise static HTML) hasn't been considered best practice for years. But then why use PHP at all, when this distinguished feature isn't usable, and neither is PHP a standardized language, nor is its stdlib any good. In fact, this retargetting of PHP with little or no architectural oversight (from an expression language into a full-blown app language with OOP and whatnot) seems endemic in the PHP world, and is also the case with eg. WordPress.
That said, I quite like the PHP community for their practical-mindedness and their get-stuff-done mentality.