Why do some people still use pure PHP if there are so many incredible PHP frameworks like Laravel?

I still use vanilla PHP for create a website, but for company we use the latest Symfony 4 just because of simple, easy to use, enterprise ready and great for collaboration with other developers.

Back to pure/vanilla PHP. I use it because of:

1. Simple, yes it’s simple, quick, fast and easy to use. Especially if your project only a one-man-show project. You know everything and you control everything.
2. Fast, sometimes framework is just make everything complicated, in the term of learning curve. We have to learn the framework convention, standard, behaviour and configuration. But this is will be easy to tackle if you understand pure PHP, understand how HTTP works, how other component that used by the framework (composer, webpack etc etc)

Routing? I just create routing on Nginx/Apache/webserver level and throw it to a PHP script.

Multiple database access? I just use pure connection as many as I want. Usually in framework we have to learn first how to use multiple database connection, each framework sometimes use different way/configuration.

Caching? Just use any platform you want and install the PHP extension for it. No need play with composer install etc.

PHP Version upgrade? No problem, just yum update or apt-get upgrade and mostly it will run smooth because you know the code and if there is incompatibility just quickly found just only looking into error log. If using framework sometimes upgrading PHP version will not work. But it depend on your use case. Before upgrade you have to read the docs whether you use framework or vanilla PHP hahah.

But when I use vanilla PHP I just worry about security, since security is very depend on developer knowledge about the system.

So I think you are good if you can solve/create solution by using vanilla PHP or framework. But for me I love working with vanilla PHP when only me as a developer of the project hahahaha.