This in turn also helped software like WordPress and phpBB become significantly more popular than their alternatives. They may not have been better coded, nor more secure or feature rich, but setup was a complete walk in the park. At most, you needed to set up a database through CPanel or whatever you used, then upload some files and run an installer. At least, you just clicked a few buttons in the control panel to install the system there and then.

Meanwhile, recent attempts at fancier competitors (like Ghost and Discourse) have completely failed to capture the marketshare of their PHP based counterparts because they're just more difficult to set up for the non technical individual or company. Their creators put image (aka a more 'glamorous') tech stack above ease of use, and paid the price.

PHP's ease of deployment is basically why so many of the larger CMS systems of today got popular at all.