For me one of the problem too is "paiment" in the buisness context is not only a transaction, its more like a bill with a item associated with the transaction, and for merchant they want also maximum if tracability for customer base, and to deal with taxes and all this.
And also running a node is quite costly, and its very unclear if bitcoin is an unit of value or speculative asset, which can be a pb both for the legal status of the transaction and lack of price stability, which make it hard to get popular in e commerce industry.
RE: Why Does Bitcoin Fail As a Payment System?