The article doesn't actually give a coherent answer on why.

People would generally claim "lazyness", as that is the Apple way. Why fix code when you can just sell new phones?

The actual answer is plausible deniability. Closed source software often leaks metadata in hard to discover ways so governments can deprive citizens of their rights under the law, and then claim "whoops, we didn't clean up correctly, our bad!".

Apple, like every other major tech company, goes along with it when nudged in the right direction.