Git was designed to support Linux development. Fossil was designed to support SQLite development. Those projects have very different needs. The details are the subject of a 1-hour talk and are more than can be compressed into a HN comment. Sufficient it to say that (I believe) there is room in the world for more than one VCS.
Earlier today, a support customer needed to know all SQLite check-ins between versions 3.8.7 and 3.8.8.1 that touched any of the files src/pager.c, src/os_unix.c, or src/wal.c. The answer is on this link: https://www.sqlite.org/src/timeline?from=version-3.8.7&to=ve...
Is a query like that even possible with Git or GitHub?
In fairness, I had to enhance Fossil slightly in order to support the query above. But the enhancement was minor and only took a few minutes. See the diff at https://www.fossil-scm.org/fossil/info/b2b62b8318700f9f