This supermoney represents Bezos' capacity to incentivize his fellow humans to act in concert toward a goal that he can influence. If he hoards it, then it does nothing for society. Bezos doesn't need it for his personal enjoyment either. After he leases a couple jets, buys a few homes, and pays for his staff, I doubt that costs more than tens of millions per year. Not billions.
If he spends it, then he needs to find undertakings that can efficiently absorb billions of dollars in value and still advance a meaningful goal. Space exploration is one of those undertakings. Bezos said he has been spending I think a billion per year on space travel / rocket engineering. There are few other areas that could so easily use this kind of capital. I would think that homelessness is another difficult problem that can absorb large amounts of value.
Maybe this arrangement of accumulation and philanthropy is sub-optimal, and we should instead tax capital to allocate the surplus democratically rather than allow the person who accumulated it to make the decision. Well, we already do that to some degree, with mixed results. Perhaps a little of both is called for.
In any event, I for one am pleased to see this money going to address homelessness. I don't care who is making the endowment, as long as the funds are used well. This is a serious, difficult problem, and this charity seems meaningful to me, not a purchased indulgence like sponsoring a new museum wing for example.