Great questions.

It comes down to speed. We expect money to move as fast as information, but instead it moves like products.

In meat space it's OK to work with batched 30-60 day pay cycles.

But finance needs to move faster.

The complexity and cost is in verification. Electronic records have to be verified against paper records which have to be verified against records in other systems, which have to be compared between institutions. Additionally there are many instruments with varying characteristics, and all of it has to flow in real time.

It might be unsolvable without technological innovation like blockchain.