As someone who works with PHP reasonably often, I'd say you have a very limited view of what PHP is actually used for in 2020, if you think 3 hosted blog services will replace it.
The majority of PHP usages tend to be, frankly, unsophisticated Wordpress, WooCommerce, Magento, and Drupal sites that are hacked up to support e-commerce. These needs can now be met by a vast array of ecom and omnichannel platforms.
