I noticed while installing WebEx today that the installer immediately terminated itself after popping up the pre-installation script.
Running `strings` on the installation plugin (CWSPkgPlugin.bundle) shows why - it's using a similar process to what Zoom does 
Clean up temp unziped app done: %i
Cisco Webex pkg plugin, begin init work.
Install CWS result: %i
Launch CWS result: %i
Terminate installer: %@
Terminate self: %@
Previously discussed here: https://news.ycombinator.com/item?id=22736608