Solar Cooker Distribution Models

Clearly there are fantastic solar cooker designs available. Why is it that these cookers have not become mainstream in many places in the world where the sun shines but have lost their trees due to wood fired cooking? My hypothesis is that good distribution models need to catch up with the excellent solar cooking designs. Or are there parts of the world where solar cookers have become mainstream, where solar cookers can be purchased for a reasonable, unsubsidized price, and that will last for 15-20 years of regular use? Are credit options available? The model I'm thinking about is how cell phones took over the world; there was a need, people sacrificed and today the majority of the human race carry communication technology in their hands.