Fixed income managers are only allowed to purchase fixed income products. They cant go outside of that bubble because the capital they manage forces them to only operate in bonds.
So if you go buy your generic bond fund in your retirement account there is some manager that has to source out the best bond offerings for the investors. MSTR just happens to be the best option by a mile. Their benchmark return is like 1-5% for a typical bond; now they are offered something that gives them 100%+ returns they will buy anything MSTR puts out there.
But most of that Fixed income / bond fund money will never make it over the bridge. It's permanently stuck capital that will never make it into the #Bitcoin system.