I think this shows that you do not consider all build-up options here. Let me explain that.

Could something like github be made with fossil, aka fossilhub?

I believe the answer is ... in theory yes, in practice no. So this already means, if correct, the comparison between git and fossil is incorrect here. Fossilhub would not have dominated; git + github on the other hand did. Again, in theory a fossilhub could win over people to use it (and fossil), but people will compare it to github (back when github was still great) and become quite critical when fossilhub does not offer the same or similar set of functionality. At the least the core functionality - great issues + discussions, easy committing and changing of code and so forth.

Perhaps with enough resources, fossilhub could have conquered the world, but for whatever the reason, it did not, and I think this is in part due to the design. GitHub changed how people interact with repositories. They even made it easy to e. g. add files and change them online, at a later point in time. For instance in one project I am a co-maintainer and I rarely have to use the commandline; I can simply edit via the browser as it is. I don't think fossilhub would have done the same - actually, there is not even a fossilhub, so how would you want to compare git to fossil? It's not just the commandline code. Git has github; while it is a separate project, what does fossil have that people know and use?

> It can still change, I hate the notion that because Git is so culturally embedded we couldn’t ever switch.

We all have our dreams. All desert to become forests or agriculture may be a great idea. Effecting this is hard - but best luck to you betting on fossil here. I don't see it happening. Git raised the barrier here, even if only indirectly via github.