The comparison with what the money earns elsewhere is where I’d start. If an all-cash rental nets 9–10% after expenses and reserves, versus 4–5% where I’d otherwise keep the cash, I’m interested. But that extra return still has to justify the work, risk and having the money tied up.
I’d also keep appreciation separate. Getting 9% from rental cash flow is different from getting there only if the property goes up in value.
Financing could explain some of the cash buying under $100k too. Small mortgages can be harder to find. Some buyers may be paying cash because their borrowing options are limited.