Nuclear costs the same thing whether you use it or not. If you meet the peak energy demand with nuclear you might as well save the construction of intermittent renewables.
Let's overbuild a mix of renewables and nuclear, then use the excess power to do things like green hydrogen.
Or maybe we will find other uses when electricity becomes too cheap to meter.
Unfortunately they aren't the people who drive energy policy in practice or who fund new generation (most of the time, at least).
From capitalist point of view, it's always easier to turn profit by market speculation[1], with providing gas turbine backup second.
[1] I work for considerably big wind power company building off shore wind turbines. Our main revenue source is market speculation :<