Building nuclear power stations includes a lot of labor-intensive hard to automate tasks like construction. Baumol's cost disease means it's getting even more expensive: rising general productivity leads to higher wages and higher costs in fields that cannot increase productivity as much as the general economic growth. That's why it's also still cheaper in countries with access to low-cost labor.

SMRs are a try to get out of it by building more but smaller reactors. The reality is however that nuclear has an issue with scaling down. Output goes down way faster than costs and most SMR designs have outputs far greater than what initially counted as an SMR.

Investment in renewable energy already greatly outpaces investment in fossil energy. The economic decision to keep using a fossil system is a different one than having to choose a new one. There's still problems that have no economically competitive renewable solution yet, but a lot of what you are seeing is inertia.

Base load electricity is simply an economic optimisation: demand is not flat, but the cheapest electricity source might only be able to create a relatively flat output. You'll need more flexible plants to cover everything above the base load. If you have cheap gas, base load does not make any sense economically.