PHP makes building web pages easy. I'm not so convinced it makes building web applications easy as they require another level of performance, security and tooling that a web page does not. While you can obviously write a web app in PHP (heck, you could write one in CGI/Bash if you felt inclined) there are far better suited languages to get that job done. And ultimately once you factor in the extended requirements and maintainability, what was previously seen as easy can quickly become problematic

Agreed. However, there are frameworks like Laravel that make this pretty manageable.