Earlier quoted context omitted.
Those are built by large teams with a lot of backing, and still suffer from many issues (mainly performance; Slack crawls very badly, VSCode and Discord not so much); I think it's gotten easier but still wouldn't call it "easy".
Yeah. Slack and Discord sure have enough resources to build three dedicated native apps for macOS, Windows, and Linux. Slack has been through several full rewrites yet still works terrible. At this point it must be nothing but stubbornness. It's definitely not an informed engineering decision.
Those "insanely complex apps" are... nothing but virtual lists with text and some images. You know that even first-year comp-sci students are given harder tasks?