Leveraged NASDAQ ETF outperforms 3x non leveraged NASDAQ ETF?

I was reading article an about leveraged ETFs on seekingalpha and found this:

High-beta strategies have the potential to help you achieve your goals. Of particular interest is the fact that having 33 percent of your portfolio in 3x leveraged TQQQ has massively outperformed being 100 percent long QQQ since 2010. While I think that the leveraged strategy should be run on the side rather than in your main portfolio, this anomaly warrants further investigation.

I checked, between 12/31/2010 and 12/31/2018 TQQQ had a total return of 1104.16% while QQQ had a total return of 208.86%. Which means that it’s better have a portfolio which is 33% TQQQ and 67% cash vs a portfolio which is 100% QQQ. What explains this?

The only thing I came up with is: There is a catastrophic scenario which has a low likelihood where the NASDAQ goes down 20%+. This scenario didn’t happen in the 10 years this strategy was backtested — but it could have. Because of that, the 33% TQQQ strategy is "rewarded" with high returns.