Well I think its because people have a poor understanding of margin/money management and leverage.
I think its what you describe 4xstar. Where people open too many positions and don't fully realize the risks that they are taking when they have a high leverage. I mean an easy example would be 100:1 or 400:1 on a 500 USD account.
At 100:1, a 1k lot on GBP/JPY costs approx 20 USD.
At 400:1, a 1k lot on GBP/JPY costs approx 5 USD.
Its written all over the site here to never risk more than 3% of your total account. So people go for the 400:1 and open 4 lots where as the person with 100:1 leverage would only open 1 lot. (each of these is 4% of your 500 USD account)
The trick comes in that at 100:1 with 1 lot open you are playing about 0.09 USD a pip and with the 400:1 with 4 lots open you are playing about 0.38 USD a pip. So with the 100:1 you can sustain a 5000+ drawdown, but with the 400:1 you can only sustain a 500 drawdown
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I think if you wanted to really blame anything, its that people don't sit down and take the time to work out the arithmetic. Just exactly how much drawdown can I sustain, exactly how much of my account am I using/risking if I open 'X' amount of lots, etc.
Its the same if you look at people deciding win/loss ratios instead of taking into account the risk/reward ratio aswell. So many people look for a 90% winning strategy even if its only 5 pips and they risk loosing 50 pips. But a 40% winning strategy that wins 100 pips and loses 40 pips will beat the first system. In fact the first system ends up being unprofitable over the long run.