The sad thing is that those apps' HTML and JS probably are standards-compliant, so supporting Slack, Teams, VSCode, (Electron) Skype, etc in a Firefox-based version of Electron should be possible and very straightforward - yet it probably won't happen.
What's sad is that Windows 98 fully supported desktop-based HTML+JS apps ("HTA Applications"), with access to native resources (using COM via `new ActiveXObject`) and it works with IE11 still - Microsoft just never pitched it as a serious development platform for some reason. Just imagine what today's world would be like if Microsoft did pitch HTA as a successor to VB6 (instead of the quickly-abandoned WinForms platform, now barely on life-support) (I'm mostly thinking we wouldn't be stuck with excessive memory consumption in Slack, and these apps would be able to use things like native context-menus and accessibility features)