SPXL as a 10+ year hold

I've read about how 3x leveraged bear/inverse ETFs such as SPXS suffer from decay and slowly depreciate until the point of becoming nearly worthless, at which point they reverse split and start their depreciation anew, and you can certainly see proof of this if you look at their 1 year chart. However, the opposite seems to be true of 3x "bull" leveraged ETFs like SPXL. Of course they tank in a downturn but if you hold them for 10+ years I don't see how you're not guaranteed to make a very good return on your investment. Hell, you could have bought SPXL one year ago before March's crash/downturn and still come out ahead. If SPY and VOO are considered "safe" because the S&P 500 is practically guaranteed to appreciate in value over the long term, isn't buying like $10k worth of SPXL and not touching it for 10+ years pretty much guaranteed to net you a very good return?

Let's compare SPXL over the past 1/5 years to SPY:

SPXL 1y = +47.51%
SPXL 5y = +323.85%

SPY 1y = +27.85%
SPY 5y = +94.07%

Of course timing becomes much more relevant when you finally do decide to unload your shares, but if you hold it for 10 years you're probably going to be looking at, conservatively, a 500+% increase in value. Am I missing something?