Financial services is a hyper conservative industry, and a protectionist stance is common. No institution naturally wants to share customer data with a competitor, and data custodianship is often conflated to mean institutional data ownership.
The benefit of a mandatory approach is that it often enshrines a consumer data right, which clarifies the ownership vs. custodianship conundrum. Mandatory approaches also often consider consumer outcomes first and foremost, something that is not first priority when industry is left to voluntarily design delivery and outcome.
There is ample evidence to show that without a regulatory push, certain markets are reluctant to move towards a standard open data sharing scheme of their own volition. Even in voluntary markets, the regulatory pressure to deliver open banking is so strong it might as well be considered mandatory (it’s a case of “do it, or else we’ll do it for you”).
The advantage to a voluntary approach, though, is that incumbents recognise the incentive to participate, and often see economic and commercial value from participation; the ROI is there in some form, and the business case for broad data sharing is compelling enough to participate because the majority of FIs have a similar POV.
However, experience seems to prove that a mandatory approach is needed to accelerate open data sharing at scale.