How many people even have a safety deposit box?

Many banks don't offer them anymore, and in some countries they have a disturbing tendency of getting robbed, with absolutely no recourse for the depositors (since contents are usually unverified and uninsured).

Then buy a large fire safe, bolt it to your floor inside a closet, and fill it with 10 lb barbell plates until it requires a forklift to move.

If your threat model includes someone inside your home with power tools and you can’t trust a bank… you might want to consider moving.

Given that people probably don't arrange their life around the ability to safeguard physical assets, I think you've just given several good arguments against self-custody:

Many people don't own a home. Not all of those that do want to expose themselves to the liability of storing valuables there. The safety situation between homes even within the US varies greatly, and even more so internationally. Banks with safety deposit boxes aren't ubiquitous.

If it works for you, great! I'm just saying that you might be in the minority here.

You tell me.