There are actually a couple dozen fission startups. Fission is definitely an easier technical problem, but more difficult in other ways. Nobody minds if you fuse atoms, but you can't fission them without doing lots of up-front design and spending years getting through regulators.
Some regulators are friendlier to new technology than others. Canada does pretty well, and has at least three molten salt reactor startups. Terrestrial Energy in particular is pretty far along and has high praise for their regulators.
In the US, the NRC is much more difficult, and it's practically impossible to develop anything here besides a light-water reactor.