Why can Zend not simply change the license of the Zend Engine to PHP License? Why do we want this? Because it creates issues with using PHP. And we do not even inform people about it, because we are silent about this fact. So is there a reason why this has not happened already long ago?

He points out the two different sides to consider - how they (Zend and their employees) have contributed to the language and its development and what the license says about ownership of the main engine. Andi Gutmans (of Zend) has made a comment on the post about why the licensing is set up how it is and how it relates to the TSRM library.