Then why do all traditional schools of Islamic jurisprudence punish individuals for apostasy from Islam? In the Islamic world your view is the minority view.
Not all, take Turkey for example. Also being a minority view doesn't make it an incorrect view. As to the why, because people use religion to manipulate and control others.
This punishment is not supported anywhere in the Quran, it is from extra-Quranic sources(which openly contradict the Quran). The Quran claims that:
6:38 - We did not leave anything out of this book.
7:52 - We have given them a scripture that is fully detailed, with knowledge, guidance, and mercy for the people who believe.
Now obviously the Quran doesn't contain, everything. I have not found my mothers recipe for lentil soup anywhere in it for example. It is claiming that everything that pertains to salvation is within it. So if every detail is within it and there is no mention of punishing an apostate how can punishment of apostasy be part of the religion?