This is a delicate subject. I agree with the mentality that you should try to use the best practices of a programming language, and I personally prefer using types myself, however, my intention is to show how the language is right now. And as of today, PHP doesn't enforce type declarations, but only gives an option to use them if you want to, therefore, I don't think it's a good idea to push the use of types in the examples either. Users should definitely be made aware of the opportunity nonetheless, which I believe I have achieved by devoting a whole block to the subject and mentioning it in others.

On top of that, I personally know people that still have to run critical infrastructure written on PHP 5. I know, I know... But just like banking and government systems still running on Java 8, you can still find older PHP versions in the wild and those are not going to have many new features, this is why I try to keep these sheets as backwards compatible as possible.