Ignoring nuclear for a moment, wind and solar both compete and complement each other. At a certain point, in a certain area, it stops making sense to spend money on wind/solar and start spending it on solar/wind instead. Because for the same money, you get more if what you want.

You could do similar for tidal power, but since it's so much worse than wind/solar in terms of efficiency/cost you basically don't build any.

Not because it's competing for steel, but because you have better option(s) for achieving the same goal.

Now, swap nuclear for tidal power and you have the same situation.

The main problem for renewables in the UK is the same main problem for them everywhere. Fossil fuel lobbying. All the bullshit about wind turbines was generated by the same political groups funded by fossil fuel interests.

It's great that lots of people have put a lot of effort into getting past "There's no problem", "There is a problem but we can't do anything about it", "we can do something about it but it's too expensive", to get to the current "it's cheaper but the people don't like it".

Imagine how much further on we'd be if we didn't have to wade through all that BS to get here.