People hate on PHP for a number of reasons, and that's why it's unusually unpopular. Here's my (highly subjective) take on why.
The barrier to entry for that language is extremely low, that is anyone who can manage to FTP a file to a server that has a bit of PHP in it can as much as consider themselves a "PHP programmer". This means there's an awful lot of extremely low quality PHP code out there written by people who didn't know better.
Secondly the language itself is so dizzyingly confused, where there's literally thousands of methods in the root namespace, and there's no pervading design pattern. Arguments appear in random orders, terminology changes, and functions from C, not exactly known for being programmer friendly, are simply ported, warts and all.
Then there's the problem with deployment, where PHP hosts usually have a woefully out of date version of PHP and many of the extensions that are standard have been disabled for reasons that are never entirely clear. This means writing PHP code that can be deployed on more than one host is extremely frustrating, often leading to writing it for the lowest common denominator just to avoid support issues.
Plus, there's this pervasive attitude amongst the PHP developers that frameworks are a bad thing, leading to enormous amounts of badly written re-inventions of things. People constantly write their own third-rate ORM, implement user authentication that's practically a check-list of what not to do, and seem to have a talent for mashing together different concerns in the same file.
This boils down to a nearly complete lack of leadership in the PHP world as to "how to do things properly". So long as the poisonously bad, brain-damaging w3schools is the go-to source of knowledge for PHP developers, things will only get worse.
If you like PHP for whatever reason, and surely some people do, the most important thing to help promote that platform is to be vigilant about stomping out bad development practices and setting a good example for other developers by explaining how to do things correctly using modern techniques.
This sort of outreach is taken for granted in the Python, Ruby or Perl communities which go out of their way to support aspiring developers. In the PHP world, it's full of nomads that prefer to go it alone.