Malware on macOS isn't prevalent. There is no market for anti-virus vendors on macOS, and Apple have been repeatedly tightening the approval process for macOS software. Gatekeeper only ever gets more aggressive, not less. Meanwhile videocall software is widespread, it's rapidly become a necessity for a large part of the world's population. I wouldn't be surprised if on macOS it's now in second place as a category behind web browsers.
No.
What Apple should, MUST do as quickly as possible, is understand and react to what developers here are trying to tell them - the usability of macOS software installation is terrible and no, the App Store is not an acceptable alternative. macOS software install UX is worse than Windows. It's worse than Android and iOS. It's better than Linux but that doesn't say much.
If Apple want to end these practices, they need to deliver:
1. Genuine one or two-click install of software from the web, without the App Store being involved and without requiring sandboxing, allowing install scripts and for signed/notarised software, without any security popups. DMG style installs require drag and drop AND device unmounting, which isn't especially discoverable and hardly used on mobile platforms so some users can't figure it out (hence the reliance on PKG files).
2. Removal of the scary popup that Safari shows when a user clicks a non-http URL.
Desktop software on macOS relies on these techniques because measuring the ratio of number of downloads to number of successful app starts shows that far fewer people make it through the process than they should, for instance, fewer than on Windows. This is a bit of an open secret in the desktop software world for many years now; Google for instance has detailed data on the problem. Each click you add causes the success rate to drop and macOS requires far more clicks than is justifiable. Additionally, the web server trick Zoom uses is because otherwise some non-trivial proportion of Safari users just automatically click cancel on the security popup when a web page tries to open a meeting, without even reading it. They don't understand what they're being asked or why, but figure if Apple want to double check with them it's safer to say no. Then they fail to join a meeting and if they're an important participant, that means the meeting fails for everyone.
Note that this usability problem is Safari-specific. On other platforms and browsers such workarounds aren't needed.
People need to stop giving Apple the benefit of the doubt here. Videoconf firms aren't doing this extra work because they're malicious or incompetent or because they inexplicably like doing work. They're doing it because otherwise a lot of Mac users fail to achieve the task they set out to do, and that hurts the usage of the video platform. It's ultimately Apple's problem to fix.