I agree that reasons could be many and relevant. For instance, retail payment systems are far too heterogeneous. However, the growing importance of retail payments, the increased complexities and technology driven payment systems call for a revisit. Further, there are some retail payment systems in most countries which are ubiquitous in nature and have system-wide importance.
At least in a large country like India we are talking about retail payment systems which are quite significant. Let me state a few numbers. We clear on a daily basis approximately 4.5 million cheques, operate nearly 2 million person to person electronic fund transfers, handle around 1.5 million bulk payments i.e. one-to-many and many-to-one payments.