Shutting down nuclear plants is "total madness"

The problem with nuclear is threefold: expensive, slow, blocking. In comparison to other energy sources it is expensive (build + produce) and takes a long time to build. These to factors make it a bad solution if one wants to solve current problems, thus investments in nuclear are potentially blocking better solutions right now. Small Modular Reactor etc. may be a solution to these issues, but right now new nuclear is not viable for the short term.

That however doesn't answer why they were shutdown in the first place: After Fukushima Germany decided (+10 years ago) to shut down all reactors. The plan was to invest heavily in renewables and thus create a fluent transition. The latter part didn't happen because Germans like to plan but don't like to spend. However, the plant owners still planned for the decommission. Ironically this of course coincided with the economic fallout from Russia's invasion in Ukraine. The plants were kept online a bit longer (which was extremely expensive) just in case, but it turned out to not be necessary.

On the plus side: In the last few years investments in renewables and energy infrastructure are ramping up massively. Should have happened earlier, but it's the right direction for now.

Tl;dr: It was planned for renewables to replace nuclear over time, but that didn't happen. Building new is too expensive. Keeping them online now it to expensive. Renewables are ramping up now, so this shouldn't be an issue in a few years. Still, the execution was dumb.