Why are there not more nuclear power plants than plants that burn fossil fuels?

Largely history I think, fossil fuels started to be used for electricity from 1880 onwards, whereas nuclear didn't start until the late 1950's and at first it was semi-military in its origin, true commercial exploitation didn't start until the 1960's. Then it turned out to be rather more expensive to build nuclear plants than first thought, and the Three Mile Island incident discouraged power companies from investing in nuclear, whilst the availability of natural gas and the cheapness of plants to use it encouraged that fuel to take up the extra load demand, both in the US and Europe. In France the opposite happened, without their own source of natural gas, the French decided that nuclear was the route for them and now have about 75 percent nuclear, so one can conclude that given the right circumstances nuclear can become predominant. This is probably helped by having a nationalised electricity body since Government can take economic risks which companies owned by shareholders may avoid. This also applied in the UK, the AGR reactors would certainly not have been proceeded with after early setbacks unless the CEGB had been the body buying them, and as soon as the industry was privatised and broken into smaller units (by the Thatcher government) nuclear orders ceased. Ironically, now that nuclear plants are again required in the UK, only the French or possibly US industry can supply them.