The reason is that the figures for the banking industry as a whole can mask sharply different degrees of concentration in  3  BIS Review 107/1999  specific segments of the market. In wholesale markets, competition may be fiercer and a critical mass may be required which exceeds that appropriate for national markets.
In the retail markets, on the other hand, banks still operate in fairly fragmented national markets. It is also true that for a proper evaluation of the relationship between concentration and competition, the volume of intermediation activities by non-banks in specific segments of the retail markets should be taken into consideration.