Kile,
In order to enhance user experience and strengthen accountability and transparency meeting apps are required to be attributed to a user. This requires meeting apps to authorize with the users ZAK or the Users On Behalf Of token. This means that the App user must also be a Zoom user and the user must be present in the meeting.
Using a service account’s ZAK for all app users would not allow the app to join the meeting since that user is not actually present in the meeting. In that case the app join would fail.