Because producing tools with php is VERY fast, and it runs almost as fast as a scripting language could. It's simple, and efficient. One of the language that requires the least amount of code to produce a given result. Plus the longevity of the project.

The question is why would anyone NOT want to use php in 2021 for non desktop developments?

I also prefer pure php, with no frameworks. I think it's best to build your own tool that suits you.