Simple, because no one wants to make any effort to use real multisig, dont believe me? ask any vendor who offers both.
Why though? Because multisig only benefits the vendor, who have dozens of orders built up over the 1-2 week escrow period. Buyers typically only have a few orders that are filled within 1-2 days.
Site thefts only affect a tiny percentage of buyers who only have a small amount to lose within a very short window
- Connect the dots now? Multisig may pick up in the distant future, but only after vendors unanimously start requiring it.
So how can vendors get the benefits of multisig without the downside of hassling unwilling buyers?
2-of-2
This means when an order is placed, the funds are placed into a multisig address where the site holds one key, and the vendor holds the other. This process is invisible to the buyer.
So what happens if the site goes down?
TMP solved this issue with timelocked addresses. Funds will be released automatically to the vendor in case the site disappears.
What happens when the buyers demands a refund?
If the arbitrator, the site admin, decides the buyer is trying to scam or is at fault then the buyer is denied the refund.
If the arbitrator decides the vendor is at fault then he can request the vendor refund the customer before releasing the amount to the vendor. The customer would supply the address they want to be refunded to and the admin would see this on the blockchain. If the vendor resists then the admin can take action against the vendors account and the money would be lost.
Wait but then this isnt escrow if the money cannot be returned!
This is missing the point of escrow. Its purpose is not to gaurantee refunds for buyers, its to remove the incentive for vendors to steal.
By blocking the withdraw (ie theft) of customer funds, not only will a vendor be unable to get away with a scam, but he will also sacrifice his reputation and his account.
Most vendors would not be so stupid to get on the wrong side of an admin over one sale.
To hold vendors accountable and prevent theft. This is the purpose of multisig.
Actually, it's to ensure that both parties in the transaction are held to the agreement with a third party acting as arbitrary.