It can be a hurdle in some cases like when the buyer needs instant delivery but seller makes him wait till confirmed.
If a buyer needs instant delivery, then they should not try to make payment with Bitcoin, or they should also be very much ready to pay with a high fee rate so that they can get their payment confirmed as fast as possible.
Besides, most of these sellers make use of a centralized payment processor, which you can just use the same system to pay them so that it will be easier for them, and everything happens off-chain, just like using Binance Pay to pay the seller into the seller's receiving account.