Hi Saket,
With regard to us hearing the arya dhamma; yes, I agree that we would have heard it numerous number of times. But just because one hears it doesn’t mean that he will understand it. And it is the proper understanding that is necessary and not merely hearing it. Think of all the people who hear this sa-dhamma even today but cannot understand it or merely don’t want to try to understand it or even just shun it aside and look down upon and insult it. So, all of us would have done such things in our past lives and hence even if we heard the dhamma we may not have been in a state to comprehend it.
To understand the dhamma one needs to have pragna and through samsara each one of us would have been cultivating pragna to different levels and ultimately peak when (if) one becomes an arahanth. I think this also refers to paramitha that one cultivates.
So to your question of why we didn’t attain any magga pala even though we may have heard the dhamma earlier, it would have been because our pragna may not have been developed to the required level.
This or a similar question was asked from the Buddha. According to paticcha samuppada the reason for the samsara is avijja. So, after avijja is taken off completely then there could be no reason for samsara. I cannot recall the sutta though.
On a personal note if there was a possibility that one could return to sansara after one attains nibbana, there would have been no point in the Buddha teaching all this. It is such a comprehensive solution to all problems that if such a possibility was there, I’m sure it would have been taken into account by him.
Just because one couldn’t attain any magga pala in the past doesn’t mean that he cannot attain it now or in the future. However only a Buddha will know whether someone has the potential to understand the dhamma and if so how far and what level of magga pala he can attain in this life. So we should not be discouraged and try as much as possible to understand the aniccha, dukka, anatta nature and attain magga pala. And if we have attained a magga pala to keep on going until we attain arahanth.
But even if someone doesn’t attain any magga pala in this life the effort will not be invain, as this effort will help grow ones pragna (paramitha) so that he can attain magga pala in a future life. There are also examples of instances where people attained various magga pala at their dying moments. So even if one has not attained anything yet, we have to keep that effort going.