Renewables fluctuate. Nuclear is not great at scaling, and most reactors cannot be shut down without taking weeks and months for safe re-starting.
Nuclear is good for base load. And countries that have a lot of (really expensive) nuclear to cover their base load, have zero incentive to invest into renewables, since its output would just become surplus.
For broad adoption of renewables, we need to accompany it with (hopefully clean) solutions that can buffer and restore surplus energy efficiently and most importantly scale up and down really fast, to smooth out the fluctuations. Keeping a constant 50 Hz is becoming increasingly difficult with renewables.
In the past Austria used to store (nightly) surpulus energy from german nuclear reactors and (more recent also renewables) and getting paid to do so, to feed it into the own network and also selling abroad during daytime. This was stopped because it was putting a lot of strain on the north-south bottlenecks in the German power network, aggravated by large wind farms in the north, that became capable of covering the whole German power use for short periods of time.