Adding to what others have said here, nuclear is great for base load consumption. Use the renewables to supplement during peak hours where load variability is the greatest.

Sure, you could connect renewables to batteries / accumulators for times when they are not available (i.e. no wind, no sun) but this doesn't give a very good consistent base load. A nuclear plant that is 1 MWe will always give 1MWe if it is up all the time. I'm not saying here that batteries aren't a good option, just that they aren't the optimal solution.

Another thing to consider is resistive transmission losses. Connecting long cables from, say offshore wind farms or areas of high wind density, to electrical substations long distances away makes delivering the electricity more inefficient. Granted, having it is better than not (nobody likes brownouts). But engineers try to take all of these into consideration when working on the regional power grid.