David-
1. An article with many short sections would
inappropriately get a TOC
that would waste space.
Then remove some sections.
2. An article with just two very long sections
wouldn't get a TOC but
would be appreciably helped by one.
Then add some sections.
3. Sometimes a TOC would be best located not at the
top of an article,
but after a short introductory paragraph. I think some dead tree
encyclopedias use this method.
That's the current behavior.
4. If displaying TOCs is off by default,
It is enabled by default.
Regards,
Erik