5% is not that vital an amount so the suggestion of Fidelity is more on leaning to the safer option or the lower risk option. Bitcoin is not yet very established as an investment option but it somehow suggests that it is quite independent and uncorrelated so those which are trying to diversify their portfolio won't risk much if they allocate an amount as low as 5% to Bitcoin.
It has so much potential, as obviously shown and proven by its decade-long existence, so companies are not really blindly risking their 5% to something untested.
This is just the beginning. Major funds never invest all their capital in one place. They start little by little with low interest rates. In addition, you need to look not at interest, but at the amount of funds invested in bitcoin, and this equals several hundred million, which is quite a good amount. I am sure that other foundations will follow suit.