Why is there a shortage of vaccines?

Having spent a year on developing the vaccines now on the market, it seems extraordinary that the companies involved appear to have uderestimated the surge in demand that would follow once their products had been authorised and regulated. In other words, the world's population of 7.6 billion. Ok that's daunting, but it's not quite as challenging as it sounds because at least three major countries have developed their own vaccines: India has two indigenously-developed vaccines called Covishield and Covaxin, then there's Russia's Sputnik V and China's Sinopharm. That takes care of more than 2.8 billion people. So 5 billion left. Take away the 2.2 billion children in the world's population who probably won't need to be vaccinated and you're down to 2.8 billion. Then there are countries, such as Hungary, Argentina, Brazil, Bolivia and Nepal which, fed up with waiting for the Western-developed vaccines, have opted to buy Sputnik V. Other countries will no doubt follow suit. Serbia has bought a million doses of Sinopharm and, again, China's vaccine will probably be sold to other countries. So perhaps we can say that around two billion people will be relying on Pfizer, Oxford AstraZeneca and Moderna. Although there are numerous other vaccines on the way. So the challenge is still huge but with sufficient preplanning why is it that there are not dozens of factories churning out the vaccines to meet the demand? The only reports we are now getting are how supplies are running out, some areas are not getting any at all, some countries have received such pathetic amounts they have hardly started the jabs and predictions of future supplies are being significantly lowered. Producing little bottles of vaccine is surely nothing like delivering cars off the production line. Is this not a 24-hour seven-day-week effort? As the virus itself scampers off in all different directions, varying in deadliness, the production of effective vaccines has become a race for survival. Joe Biden has called for a war effort to tackle Covid-19. The companies producing the vaccines need to adopt the same warlike approach to bring the pandemic to an end.