Why do parents promise to do something and then break their promise when it is time do step up to it?

Answer 1

Ah, children never let anything go. A parent, with good intention, will offer to buy something or take the child somewhere and when the time comes to "step up to it", as you say, something else may have come up or there may not be enough money or whatever. Try and understand that parents aren't trying to lie, they just get overwhelmed, tired, out of time or money, and a zillion other reasons. Parents, however, should never say "I promise" unless they are 100% sure they can come through.