Nuclear power plants take a very long time to build, it can be 7-10 years before you even begin construction due to all the permits, politics and planning.

As for scaling massive amounts of solar/wind... that's exactly what China is doing to power their infrastructure buildouts.

7-10 years to scale it right is better than immediately doing it wrong in my mind! Or what China is doing if they really just can't wait to scale (though my understanding is China is still increasing the total amount of power generated via coal even though the percentage of power generated via coal is going down - so not quite the full step needed).