Self-imposed isolation and deadline.
> without having input either from navigation apps or from consumers
Because Apple never asked either navigation app developers or consumers since "Apple knows best" and spent several years fighting DMA instead of implementing these features.
> Websites and apps still integrate with a navigation product directly, rather than use this scheme.
Because there was no scheme to begin with, and when Apple finally relented and made it, it only made it available in the EU.
> Until everyone is sitting at the table wanting to work towards interoperability, the feature simply can't work.
Yes, Apple doesn't want to sit at the table to work towards interoperability.
Apple Maps was made default on iOS in 2012. They literally only implemented the "scheme" last year, 13 years later.
DMA entered force in 2022. Apple had known about it coming for at least two years before that.
And even without DMA that would be a proper thing to do to begin with which they had to be forced to do by government action.