Why should they? It's not the right time for that yet. Letting the price stay high despite renewable prices being lower means it's tremendously profitable to build new renewable sources, so there's lots of incentive for it to be done.
There's no incentive... Why invest in a less reliable source if you could endlessly purchase gas power for the same price? It slows the transition from fossil fuels and ensures that oil and gas never takes a loss.
I believe that no governing party has attempted to fix this. Generally - this set up benefits the oil/gas lobby, so efforts to change it will butt heads with them. UK also trades energy with mainland Europe, which can add a complication with how prices are set.