Usually there are limitations by payment method providers, such as
1) such as authorization as was mentioned by others,
2) paying to accounts from abroad typically involves higher transfer fees,
3) not all payment methods supported (for example what is available in the US, might not be available in Japan or Russia),
4) transfer times via conventional bank wires can take days or even weeks to be processed,
5) in the case of scams, it's way harder to resolve issues on international scale when banks are involved, and can take 1-2 years (actually saw that happening).

That's why due to above, on as.exchange for example, you can always select "Other" as a payment method and type whatever you prefer, or even pay with crypto for the BTC (for example can pay with USDT, BNB, ETH, or anything else), which helps it to serve as a secure crypto-to-crypto escrow to whomever needs that.