There are many reasons why a country will try and diversify its energy production, the main objective is the continuous and stable production of energy, because the economies and essential services of modern society rely so much on electricity dependant functions.
For example if a country’s entire energy output relies on one source, and that source is interrupted or depleted it will no longer be able to produce electricity, crippling services, industry as well as the economy. The mark of a modern developed country is the ability to provide safe and stable electricity to anyone that needs it, and this is a factor in why some companies chose to set up in the UK for example.
A investment in renewable is more a investment for the future, as non-renewable energy sources are cheaper in the short term, but eventually will run out, and as renewable wont it makes them eventually essential.
Green peace for instance wants the whole of the UK’s energy to come from fully renewable sources, and minimize pollution completely; they want this to be achieved over the next 20 amount of years, on their website they even say...
“Between them, wind, wave and tidal power could deliver more than twice as much electricity than the new fleet of nuclear reactors being debated - and the renewables would be built more quickly. Even then, the full potential of these sources would not have been tapped - much more could be harnessed in the future. But we have to start now if we're going to end our dependence on fossil fuels and reduce emissions. Ambitious support for renewables will bring benefits - not just of clean, fuel-free energy, but the jobs and economic growth that come from pioneering new industries and technology.”
Source From Green Peace
Another good reason to diversify is the fluxuations in global prices of raw materials, for example since china increased its use of coal power the price has rocketed, making coal suddenly more expensive plus increased demand with clean coal technology increases price even more.
So if a country has a range of different energy sources it won’t be as affected by sudden increases in for instance oil or gas, these two tend to change the most, for many geo-political and economic reasons.
And as for political motives, it is political pressure from pressure groups than force the government to spend more on renewable and to subsidize new technologies, this is because the government wants to keep these groups happy and appear to be doing the right thing in terms of the environment.
The future of energy generation is unclear but exciting, as a whole range of new technologies emerges from various companies, governments and scientists.