Yes, it is intentionally excluded, since it would rarely be inserted directly, but only indirectly as a side effect of importing a web page, document, etc.
You can override the default behavior via a registry setting -- see CanInsertDocumentTemplate at
https://kinook.com/Forum/showthread.php?t=5097.
The reason that Task is spelled Tas&k is so that if you use the keyboard to show the context menu, you can press k to choose that template item with a single key and not have a conflicting mnemonic with the Text template. You can rename the template item if you don't want this behavior.