Because, y'know, communities actually exist, like, in the real world. More relevantly, they have a fairly important goal in protecting real, actual people from bodily harm and providing a nurturing environment for them to thrive in. Since this does not apply to virtual, Internet sites, calling them "communities" is quite misleading and can have bad side-effects if the metaphor is taken seriously, either by accident or through sneaking connotations. So I think it's better if folks are sometimes encouraged to taboo this particular term.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
Notes for future OT posters:
1. Please add the 'open_thread' tag.
2. Check if there is an active Open Thread before posting a new one. (Immediately before; refresh the list-of-threads page before posting.)
3. Open Threads should be posted in Discussion, and not Main.
4. Open Threads should start on Monday, and end on Sunday.