MicroStrategy Inc., already well on its way to transforming from a software company into a bitcoin repository, just sold junk bonds that give investors a novel way to put money into the cryptocurrency. The question on Wall Street's mind, though, is why there was so much demand for the debt when there are more straightforward and potentially more lucrative ways to invest if bitcoin ever makes it "to the moon"—like just buying bitcoins.

Nevertheless, MicroStrategy had an easy time with its offering Tuesday, the first-ever junk deal to fund bitcoin purchases. It originally planned to sell $400 million but had orders for all of that even before officially launching the transaction with a solid presence from hedge funds. It boosted the offering to $500 million and locked in lower pricing.

Some of that demand came from investors who want bitcoin exposure but can't buy the digital coins outright because of how their funds are structured, according to a person with direct knowledge of the offering, who asked not to be identified discussing private details.