The top open-source ecommerce platforms (magento, woocommerce, etc) and content management systems (wordpress) are all in PHP, and yes they were written before 2000. You don't need to know PHP to be a successful web dev if you are working at a silicon valley tech / social media company, but e-com and content management are still what most companies are trying to do on the internet, and if you are interested in a tech career outside of silicon valley, being handy with PHP is great.