You miss the point. You can't mug someone for their Vanguard account. Robbery risk is limited to cash on hand, or arguably whatever the ATM limit is on your bank account.
Like crypto, wire transfers are difficult to track and irreversible.
The victim may also have a chance to cancel the transfer, because they’re not instant. (especially outside of business hours)
It’s just not an attractive way to mug someone, it’s easier to take them to an ATM.
In Europe a wire is instant with no recourse.
Most banks have processes for giving money back in some of these cases.