The 'read more' function in Joomla has a long, somewhat important history which has effect to this day. In Joomla 1.5 there is only one editor when you open an article. Underwater (i.e. in the database) there are however 2 fields where data is saved, one for the intro and one for the main content of the article.
When we are using F2C to create a Joomla article we need to 'fill' both database fields. To do this we require two separate F2C templates. The f2C intro template and the f2c main template.
In Joomla the 'read more' link is automatically shown when an article has both an intro text and a main body text. This is created by adding the Read more tag in your article content.
Why does it work this way?
There are two reasons why F2C works this way. First reason is the above one and can be seen as Joomla legacy. The second reason is more important. We want the web developer to determine where the read more tag is added, not the user. Just because Joomla works this way doesn't mean it's logical for an end user.