I think you're putting too much faith in frameworks there. My employer's large PHP application is written in a framework that was once popular but then was abandoned years ago. Since that framework defines every aspect of the application, down to the directory layout, migrating away from it towards a more recent framework is largely impossible at this point. While it's true that the framework is "easy to understand", it's also true that it encases the application like a concrete coffin.

Libraries are infinitely preferable to frameworks if you want your application's life cycle to be independent of $POPULAR_FRAMEWORK's.

Even with Laravel, which is the current thing in the PHP world, I've worked in multiple teams where their application is written in a very old version of Laravel and there's no desire to attempt an upgrade to the most recent version.