Mining the Bitcoin was never the hard part. The hard part was always not selling it for massive gains because you don’t care about the money and then watching it become more money than you need. The type of person who wants to go back in time to make easy money is the type of person who would still cash most of it in early to spend before it turns into something life changing. It isn’t opportunity people lack, it’s greed that puts a ceiling on how high they can go.
I believe that setting up the mining equipment, which is highly expensive, is another challenge in mining bitcoins. If that money had been invested in bitcoin back when it was first created, it would have changed the investors lives for good by now.
Just as you stated, greed is the primary obstacle to all of this, as the majority of people had the chance to buy early and could have reached another milestone today, and if they continue to hold, I believe it will lead to a significant profit in the future.