Why is using the cache tag more expensive than outputting static text?
Since the {% cache %} tag solely stores its information in the database, it has a guaranteed minimum of one database call to make to see if what's inside of it has already been cached.

If you're just doing this:

{% cache %}
    Hi. I'm static text.
{% endcache %}


That's quite a bit more overhead than simply:

Hi. I'm static text.


With no real benefit.