Iran nukes

I have searched the Internet on numerous times to find an answer to a question that I have posed on three different occasions over the past several years and I have yet to find the answer. Iran has been trying to enrich uranium for more than 20 years and as yet has not succeeded in making enough for even one nuke. During that time North Korea has made a number of bombs. In about 5 years, back during the 40's, the US made the first nukes using technology from 75 years ago. Every one is aware of how much technology has advanced over these years, yet Iran is still not able to enrich the 35 pounds of U-235 needed to make a bomb. If they wanted enriched uranium North Korea who is in desperate need of cash would have gladly sold them some. I maintain now as I have over the years, that they did not want to make a bomb. That is the only logical explanation of their apparent ineptness. They have always said they were not trying to make a nuke. They have endured sanctions because they refused to allow complete inspections. It is a conundrum that is baffling. Perhaps there is something else that they don't want inspectors to see.