First it could be something depending on you enrolling like airport fastpass and second it would be a feature that it is complicated for both side to record and process the info so that they have the incentive to do the minimum possible.

But don't be naive, clearly US is not pushing so strong on this feature that it is clearly not just to facilitate your travel and reduce processing time but because they know that they will be able to tap as a friser in the best biometric database of foreign citizens that they could.