I agree with the point you're making, however for some reason on Linux, desktop environments usually are far more extensive than that.

KDE, GNOME, etc. usually don't only consist of an app launcher, but a file browser, text editor, archive manager, browser, image viewer and who knows what else.

I never understood this tribalism, doesn't the spirit of open source mean that I'm free to choose the tools of my liking, may the best tool win, etc.?

This certainly the case on Windows, where people usually just replace tools to their liking.

Most distros usually strongly push the desktop environment's native apps for every niche.