Actually you can't blame those early Bitcoin investors who sold their Bitcoin way too early because just like some people are gambling on altcoins now that was basically how the early investors where doing same with Bitcoin because it was just a coin that was new into the market so no one would have given their 100% trust as at then and it's almost impossible to trust any system that just got introduced and has not gotten much attention and recognition by a large number of people
As the matter of fact I don't even consider that as an excuse to those early investors who sold a large amounts of there Bitcoin then because there is no way you will presume that the reason why they sold there Bitcoin then was because they did not trust Bitcoin, however in that regard there is no how somebody would invest on something they did not trust or believe on, so actually I don't think trust was the reason why they choose to sell there Bitcoin, however the only way we can justify their reason is that during those days most of those people does not really understand the importance of holding so instead they were more focus on collecting the small profit they saw on there investment, however in as much as we are emphasizing on this case let us not generalize it because there are also investors from those days that are still holding till now.