It may make more sense once you realize Fossil development started in 2005. Quoting https://fossil-scm.org/home/doc/trunk/www/history.md :

Beginning around 2005, the need for a better version control system for SQLite began to become evident. The SQLite architect looked around for a suitable replacement. Monotone, Git, and Mercurial were all considered. But at that time, none of these supported sync over ordinary HTTP, none could be run from an inexpensive shell account on a leased server (this was before the widespread availability of affordable virtual private servers), and none of them supported anything resembling the wiki and ticket features of CVSTrac that had been found to be so useful.

This is three years before GitHub was founded, and long before tig was released.