Still 80%+ of PHP sites.
https://w3techs.com/technologies/details/pl-php/all/all
https://www.linkedin.com/pulse/ticking-php-time-bomb-martin-...
5.6.36 was released in April 2018; 5.6 was released in 2014. 5.1 was released in 2005 by contrast.
There's nothing terribly wrong with running 5.6x if you have a good reason to do so (eg legacy), other than that the performance sucks compared to 7.2.
You can dig further into the w3tech numbers here:
https://w3techs.com/technologies/details/pl-php/5/all
Nobody is using 5 or 5.1. The majority of all PHP installations are using more modern versions, either 5.6x or 7.x.
PHP needs to go away.
And from sitting in on a lot of leadership meetings, they're one of the few groups that perpetually seems to be concerned with something they depend on sunsetting.
As long as they're passing with ISO, I just stay out of it.
Php is a go-to route of getting a shell.
And the only reason you see more vulnerabilities for CMS's written in PHP is because the most popular CMS's (Wordpress, Joomla, Drupal) are all written in PHP.
We'd see the same thing happen regardless of the language (except maybe Ada or Rust. They do a good job at stopping you from shooting yourself in the foot).