The 144,000 is a symbolic number, it has a numerical value of 9 and in several religions it means, completion. The completion being so profound that it takes the number twelve that has been associated with special followers and the Disciples of Prophets, Jesus being one and multiplies it by itself and then 1000 to show the effect that the events of Revelation will have. It's not literally a number of people.
A prophecy is fulfilled when all the ingredients come together, that fulfilment then may take hundreds of years as humanity adapts better practices of social engineering, justice and equity. Prophecy is for humans to fulfil.
