The problem with all the pre-election promises is that they are made in the circumstances, economic social, international of the time they are made and I wll grant all parties the trust that they do mean them at the election
BUT
no political party has a 100% correct firtune teller who can tell them what will happen next month, let alone six months or a couple of years down the line.
Back in the 1950s the Conservative Prime Minister, Harold Macmillan was asked what was most likely to knock governments off course. His reply was 'events, dear boy, events' and that is the problem.
Economic circumstances have changed over the past year, after years of underfunding our defence, the Ukraine war and other events mean, that most countries are having to increase there defence spending. Growth has been slower and inflation higher. The government has to take all these things into account.
Circumstances have changed and policies, even promises, have to be changed, otherwise the situation will get even worse.