I think about a great opportunity people had miss when Bitcoin was still in a lower price, imagine how many people Bitcoin would have made a millionaire, though by then most people were a bit skeptical about the growth of Bitcoin, if it has a good potential or save to invest.
People miss opportunities all the time, all of us on this forum as well. It's to say years later "I should have bought that thing", but it's also pointless, there is nothing you can do about it. The people who should maybe feel a little bad about the missed opportunity are those who somehow knew about bitcoin but for reason decided it wasn't worth the risk. In that case probably the regret would be pretty big.