Glifter, the reason is because of peak oil. We are now pumping oil out of the ground as fast as we can, and we cannot meet demand. Even Saudi Arabia has no more room to increase production. What this means is that no matter how much solar and wind we produce, it isn't going to stop oil production. It isn't going to "replace" the energy we get from oil. It is only going to add to the total amount of energy we consume. Renewable energy held out the promise in the early years (1960s) of being an actual *alternative* to oil, meaning we used renewables INSTEAD of oil, and left the oil in the ground. Today, because we are hell-bent on economic growth (and because we are pumping oil out of the ground as fast as we can and still cannot meet energy demand), renewable energy will not reduce at all the amount of oil we consume at all. Not one iota.
Another way to look at this is that wind and solar provide such a small energy flow-through that it cannot make up for declines in oil production. If renewable energy provided a high "Energy Return on Energy Invested" and a high flow-through rate, than we could use it RATHER THAN fossil fuels to run our growth economy. (We would already be doing this, in fact.) But that's not possible. Instead, Obama has ok'd the construction of 30 new coal plants, further exacerbating global warming and civilization's demise. The reason he has approved coal is because coal provides a much higher flow-through rate and EROEI than renewables, and will hence contribute much more to economic growth.
I hope you are understanding now. The problem is that we are hell-bent on growth, and as long as we are, we will be forced to use high flow-through energy sources (which are only fossil fuels). Renewables are low-flow through and cannot provide more than a tiny percentage of the energy we need to have a growing economy. Hence, as long as we have an economy of growth (debt, interest, etc), renewable development will only ever be *supplemental* to increased development of fossil fuels. What we need is to STOP GROWING, to LEAVE THE OIL IN THE GROUND, to BAN NEW COAL PLANTS, etc. We can't do this overnight, but if we keep fighting wall street, and keep presenting a new paradigm for society, we might actually start conserving energy. We might be able to leave some of the oil in the ground, rather than pumping it and burning it as fast as we can. But developing wind and solar won't slow down the pumping, because wind and solar can never meet the demands of a growth-based hyper-consumer society.