The Zoom and BlueJeans apps are both signed, which indicates they're part of Apple's Developer Program, and thus bound by its terms.

If you want to distribute an unsigned app and guide users into bypassing Gatekeeper for it, by all means, do so... but that's not what's happening in this case, nor is it particularly common due to the intentional hoops they make you (or more accurately, every single prospective user of your app) jump through.