why manifestos?

This could be a trivial matter that i am taking up in this election when we have much more important issues to discuss, but that's the fun in being a (um)"writer" whose opinion no one reads!
Election manifestos brought out by political parties are a book of promises by the parties contesting the elections. They are also things which are read by no one at all, which makes me wonder if the same manifestos with a few improvisations are released before every election. (Observation that has no relation to this post: Is it just the lack of funds that the Third Front has no manifesto or is it their way of saying what everyone knows, they have no vision hence no promises to make, they just want power to make Delhi more corrupt than it already is.)
During all the election frenzy, one thing struck me, why do we need election manifestos in the first place? They are futile not only because they are a criminal waste of paper and ink but also because we have a set of well-meaning provisions in our Constitution called Direcive Principles. Now, my point is why don't political parties promise to implement Directive Principles rather than promising rice at Rs.3? The DPs(Directive Principles)are a fair means to achieve the end- self suffiency of the people(of which accessibilty to food is basic). For instance art. 39(a) reads the state shall direct its policy towards securing adequate means of livelihood to citizens, if this is promised to be implemented, we not only have the problem of rice accessible to all but it would also take care of other basic needs.
The election manisfestos should simply be about implementing DPs, because only their implementation would bring about true democracy. We can't rubbish them of as outdated when most of our population is langushing in poverty. And certainly, poverty aleviation is more important than say, free television sets! I rest my case.