It is often stressed in WordPress circles that plugins and themes should be compatible to obsolete 5.2 version of PHP programming language.
Because otherwise you will break people's sites.
Because people still run their sites on PHP 5.2.
Because they don't know they should update.
Because we won't tell them.
Because they don't have to know.
It took me a long time to grasp that "they don't have to know" is one of the most important and least obvious WordPress principles. I don't agree with that.
Hard, cold, sad WordPress truth. And I fully agree with it. "You have to know." But how to do make people care? They will only want to know if they care about their site.