That's more or less what they are doing. Most of the reactors that have been shut down were built in the 1970s when safety standards weren't as strict as they are today. https://cnpp.iaea.org/countryprofiles/Germany/Germany.htm That is, the reactors were over 40 years old and were reaching their end-of-life dates anyway. Upgrading them to conform to modern safety standards isn't cost-effective.

Essentially, this is what the nuclear phaseout entails; old plants are decommissioned and governments refrain from subsidizing the construction of new ones.