There's two reasons they take so long: large plants need to be redesigned as conditions on the site develop (soil type unexpectedly changes as excavation occurs) or regulations change during the process, and the second reason is that there's basically no nuclear construction industry.

The benefit of an SMR is that it can theoretically be built largely off-site without the same risk that larger plants have wrt needing to customize everything. That allows construction companies to centralize and reuse talent and suppliers rather than needing to drag them all over the country or subcontracting to people more accustomed to building offices.

In areas like where I live, there's weeks or more of time in winter where every day is overcast, short, and has little wind. To go completely renewable, we would need to pay southern regions to overproduce by triple digit percentages of their needs and then send the energy to us by HVDC that don't exist yet either.

A bad ice storm or tornado could leave millions without any power at all at the most dangerous time of the year to not have electricity.

It's doable, but we are a long way off and if SMR miraculously hits the right numbers, it'd be a better fit for us. Until then, we'll keep burning gas supplemented with solar.