PHP has its tentacles all over the web: WordPress and Drupal are immensely popular for simplistic sites and short-lived promotionals, Magento and WooCommerce attract many e-commerce users, and Symfony/Laravel handle the custom stuff. I've worked with all of these and have the scars to show for it.
All popular projects have swarms of consultants offering advice, prebuilt additions, and custom development. (E.g. WordPress plugins and themes are everywhere.) This is also a significant factor for the penny-pinching customer — from their point of view, they avoid vendor lock-in and expensive development this way. (Spoiler: it rarely works out, in the end. "Tower of Babylon" and "shallow learning curve" mix in very exciting ways.) So there are masses of people who know the basics of PHP and call themselves "PHP developers". In my opinion, just a fraction of them actually deserves that title.