First, the theory of coalitions should predict that old organizations should be more bureaucratic than younger ones. (...) When organizations get started, their employees are not yet tied by a network of relationships (that is, cliques are not yet fully developed).
When the organization matures, there is always at any point of time a substantial fraction of employees bound by their previous personal commitments. Thus, allowing employees to exercise discretion becomes more hazardous.
(An alternative explanation for the development of rules over time is the idea that experience allows for a better description of tasks and, therefore, reduces discretion. This explanation, which does not involve coalitions, is certainly relevant. Let us, however, also note that it should not lead to the perception of rules as the lesser of two evils).
Second, the theory of coalitions may well predict that large firms should be more bureaucratic than smaller ones. The direct control of the veracity of one level of supervision's transmitted information—or, equivalently, its correct use of discretion—becomes harder and harder when the (vertical and horizontal) span of control rises.
Large banks are usually older than small banks, which also means large banks must be more bureaucratic. A bureaucratic organisation may work efficiently but there is one important shortcoming. According to Tirole:
Rules are thus impersonal (suppress face-to-face relationships) and involve a loss of information. Bureaucracies are organizations mainly run by rules.
This is probably the reason why banking and finance is much more decentralised than, e.g., the automotive industry. This is unlikely ever to change.
Source of Tirole's quotes: Hierarchies and Bureaucracies: On the Role of Collusion in Organizations. Jean Tirole, 1986