Many reasons.
1. Cost. Solar Photovoltaic panels and systems are expensive. They also require a significant amount of realestate if you want a meaningful amount of power from them.
2. Life expectancy. Solar panels have a life expectancy of approximately 20 years. simple payback without government incentives often far exceeds 20 years.
Here is some homework for you.
A fair size Power Plant can generate 1,500 MW of power.
At around 150 W per panel how many solar panels do you need to replace this one plant?
answer: 10,000,000 panels
With each panel taking approximately 2 square yeards of space, more if you have tracking and proper maintenance clearance, how much land do you need?
answer: 6.46 square miles
The City on Cincinnatii Ohio has multiple power plants with this capacity to provide power. For this example lets amd to keep it simple say 10x the plant identified above. How many square miles of land is needed to repalce these?
answer 64.6 square miles.
I hope you are starting to understand. Lets add a couple more things.
Panels if you are lucky will only produce about 80% of their rated power.
Now we need 80.71 square miles of panels.
Panels do not produce so well on cloudy days.
Panles do not produce so well at night
The city of New York would require about 15x the number of panels.
So Cincinnatti plus NY city = 1,291.32 square miles of solar panels are needed.
Oh, BTW we still need land for farming, for trees, for grasslands, for rivers and lakes etc. We also still need land for roads, homes etc etc etc
I hope this helps.
It still takes a very large surface area to supply little solar power. For this reason, it would be impossible to centralize solar power for a community with the technology we have now. You'd need a HUGE area. With the technology we have now, solar works better when implemented by the individual. It's expensive and often isn't enough to completely meet the power needs of a household on it's own. People often supplement with wind power and using some power from the grid too.
Also, solar energy needs to be stored for when it's dark. Batteries are expensive and still suck and pollute for the most part. Using solar power to break down water into hydrogen and oxygen and storing the hydrogen for fuel is a possibility.
It is being harnessed to it's potential. Solar cell manufacture is increasing much faster than oil drilling; it just started later and will take many decades to catch up with and pass oil.
And it is not free. Solar cells cost a lot to make, and (contrary to popular belief) do not last forever (a long time, but not forever). The cost of making solar cells is getting lower (due to Billions of $ invested mostly by private industry into reducing the cost). The cost of the solar panels is now less than the "other" costs (electronics, wiring, hardware, and labor to install it) of a new solar power installation. I already see solar panels on countless roofs around town, with more appearing every day.
I just hope hydraulic fracturing does not make natural gas SO cheap that people stop buying solar panels and just burn the gas instead.
There are a lot of reasons:
1. Politics, the powers that be play games with energy.
2. Money, the power companies that are in business already are watching their own wallets.
3. Cost, it has not become cost efficient
4. Reliability, it is not 100 percent all the time.
5. Size, solar farms have to be huge to accomplish any real benefit
Do some research. It is neither green nor free by any standard. The cost per kilowatt hour is very high compared to conventional methods of generating electricity. When the solar panels are no longer useful, disposal and recycling are problematic since the materials they are made from are harmful contaminants It seems proponents of "green" energy always forget to mention such things.
Why don't we all dance with the elves and fairies and have a cup of cheer why we're at it. Because to live we need more energy than toys can provide. Of course if you want to get rid of 90% of the population than we are in good shape.
Solar energy is available for free, so why don't we harness it and say bye to pollution and go green
