Well, they basically concern themselves with the ranking and when an unpopular lang hits an historical high or low, they make it into headlines. Just for the record, this month's headline (for the sake of Scala's position)

April Headline: Java back at the top!

Java is back at the top of the TIOBE index after one and half year. Androids ongoing success is probably the major reason for Java's revival. The Java language has been in slow decline for many years now, mainly due to its waning foot print in the enterprise server back end market. Since October last year the increasing demand on Java Android programming has exceeded this decline, thus pushing Java more than 3% during this period. Another interesting move this month concerns Scala. The functional programming language jumps to position 25 after having been between position 30 and 50 for many years. Scala seems to be ready to enter the top 20 for the first time in history.

Except that #14 is for April 2014.

The Tiobe score for F# improved by +0.23% (which might be from March 2015 to April 2015).

afaict the data tables for previous months are unavailable, and not recoverable from the Internet Archive because of the way the data is displayed.