Because I'm not smart enough to ride this particular tiger, and I prefer to sleep at night. The problem with bubbles is that they appear liquid up until the point they pop. Most "investors" in Bitcoin have no idea what "market liquidity" means and have never seen a "no bid" market.
All bubbles look "healthy" as long as "greater fools" keep rushing in. That's what fuels parabolic rises. As soon as that well dries up things can get very ugly very quickly as greed turns to fear and "the herd" panics.
To anyone who's made money. Congratulations. I'd advise you to remember Bernard Baruch's famous quote when asked the secret to how he got rich on Wall Street: "I sold too soon".
Haha!