Mainly because the market was fragmented and FX had a lot of arbitrary laws (i.e. which currency pairs can be traded, which pairs have a peg against the dollar)

Mainly because the market was fragmented and FX had a lot of arbitrary laws (i.e. which currency pairs can be traded, which pairs have a peg against the dollar) and also the complexity of settling cash trades. Looser regulations and burgeoning global trade have provided the impetus for the automation in the FX business.