This question has been answered by rx2. See the first response.
Do you mean no Template Variables tab? If so, this happened to us as well, even though we had TVs assigned to the article post template (your screen shot is of the article container I presume since it uses the sample.Articles.container Template) but anyway, after 11 hours of combing through permissions, code, etc. we discovered that the TVs we were using were inside of a category. The moment we dragged the TVs outside of a category (i.e. to the "root" of the Template Variables section in the Elements tab) then the TV tab showed up in the Article container. Our senior programmer said something about the current version of Articles not being able to parse TVs in a category.
Well I'm confused because there is no Template tab. There's a template field that we can see in your first screenshot. As for the Template Variables tab, it rarely is present for a resource using the articles container template, but can be present, or usually is, for a resource that uses the article post template (I forget what it's called off hand). The TV tab shows up when tvs are assigned to a template. If there are none, you won't see the TV tab. If there are, you should see it, but I don't believe the default TVs that come with articles are assigned to the container template, just the post template. You'd have to create a new post to see.
Right, yes, I forgot the Articles container has that, so different issue then we had. I have no idea why that wouldn't be showing.
If your screenshot is the article container resource, you're missing more than just the Template tab. Your screenshot is just a standard non articles type of page. When you created this page you selected "Create Articles Here?"
I usually click the root icon in the Resource tree (i.e. the World icon) and select Create -> Create Articles Here. Clicking the + button doesn't appear to allow you to create an Articles container.