You're conflating two different arguments: not using modern tools, and not accepting outside contributions. It's certainly possible that limiting contributions to a set of trusted contributors helps things move smoothly.
However it's not clear at all that using old tools has the same effect.
Also, Fossil is essentially implemented _in_ SQLite. Fossil is used to develop SQLite which is used to implement Fossil. It's a virtuous cycle. For the SQLite project, using Fossil is obviously superior to git. This doesn't mean that arbitrary projects should use Fossil over git.
The opposite can be said though, but git arbitrarily won over a bunch of other DVCS systems (another e.g. hg), mainly because of bandwagon and marketing.
I have some of my great-grandpa's carpentry tools, and I use them often. I guess I should go out and replace perfectly good tools with new stuff from a big store like Home Depot or Lowe's?
People forget that Stanley #4 plane hasn't really changed in over 100 years. It's still one of the best tools out there.
We dumped CVS because it was a poor tool, for the time. Subversion was better. Then completely distributed systems became better, because connectivity and computational power came about.
However it's not clear at all that using old tools has the same effect.