Here is a chart which includes nuclear and other zero emission technologies. A 7% difference is nice but it's a drop in the bucket when you're increasing the renewable share by 5% annually. Even if you consider that Germany shut down 75GW out of 150GW then a 15% difference is still just not very important but it makes Germany look very bad in the short term. Give it 10 years and the zero emission share will be somewhere around 90%, meanwhile any nuclear plant planned today will only be finished in 2029 only to become obsolete the same year.
The thing is that if they didn't shut down the nuclear reactors they could have shut down more coal plants. Doing so would be more environmentally friendly. And I doubt there's any serious academic that would disagree. Shutting down coal before nuclear.
The reasons to shut down coal and why it goes so slow are political. It's jobs in the east where right-wing populists are already taking over for example. Same goes for the region in the west where shutting down heavy industry and coal has been a continues issue for politicians for the last few decades. There is also the matter of contracts and reimbursing plant owners.
[0] https://www.energy-charts.de/ren_share.htm?source=ren-share&...