Staying out of election arena

I have been thinking pretty loudly for some days as to what for the political parties are there. It is generally said and believed that political parties are formed to contest polls and seek power to work for the welfare and well-being of the masses on the basis of promises and commitments made in the election manifestos with the electorate.
And, if any political party is not interested in contesting the polls for reaching the National and Provincial Assemblies to represent the peoples there, then in all fairness what is the point of its continuing to exist.
I say this because a number of Opposition parties mainly those forming not so old political parties alliance, All Parties Democratic Movement (APDM) are not taking part in the general election scheduled to be held on January 8 next year on this and that account. Not only APDM member parties are themselves staying out of the election arena but MMA's Qazi Hussain Ahmad and PML (N)'s Mian Nawaz Sharif are also pursuing Maulana Fazlur Rahman and Mohtarma Benazir Bhutto not to contest polls.
If the political parties are not contesting the polls then what for these are existing at all? Parliament is an important forum to raise public interest matters, suggesting measures for welfare and well-being of the masses at large and more importantly maintain checks and balance on the performance of the federal government of whichever party/parties it is. I am afraid if the APDM member parties stick to their decision of boycotting the general election, they would be losing an important forum and also may loose the support of their electorate in the process of negative thinking.
After all, PPP and JUI (F) are also the Opposition parties which are contesting the polls quite enthusiastically. They do not want to give others an easy walkover taking full advantage of the election being held and not many opponents in the field.
If PPP"s Mohtarma Benazir Bhutto and JUI (F)'s Maulana Fazlur Rahman are being commended and appreciated for their positive thinking and stance, others negative approach can only be deplored.