...I was about to write a reply saying "well in that case I don't understand what the GP is complaining about", but then I opened up the installer again.
I didn't fully take in what the parent was saying. Zoom is completely short-circuiting the normal macOS package install flow. You click continue once to acknowledge that "this package will run a program to determine if the software can be installed", and then Zoom is suddenly installed and the installer exits.
I can understand why they did it, but it's not good.
Although, Apple deserves some blame here. Firstly because their non-app-store software install flow has been screwed up since the release of Lion, and secondly because why can't you use Installer's "Show Files" option before the preinstall step?