Hmm not entirely sure what you mean.

When MicroStrategy issues a bond it’s typically at a very low interest rate (sometimes 0%). And the proceeds are used to buy Bitcoin so I guess they’re betting Bitcoin will grow faster than that low interest rate

Investors are willing to buy those bonds at low interest rates because they can be converted to shares of MSTR at a certain price. I.e. they can buy $100 worth of these bonds, have essentially no risk of losing their initial investment (in nominal terms at least), but they still have some exposure to the upside of Bitcoin. If bitcoin rips (likely so does MSTR) they can convert their bonds to shares at a profit.

The convertible bonds are just one of the securities MicroStrategy issues though. They have the common stock, MSTR, and now a variety of preferred stock which kinda sit between equity and debt e.g. STRF, STRK

Which gets kinda complicated, but they’re goal in issuing these securities is always to increase bitcoin per share

Sorry for the long message, hope that makes sense