How do you make identity a real platform product when nobody owns the budget?

We have been talking about identity as a product internally. Treat it like any other platform. Clear backlog. Dedicated owner. Roadmap. SLAs. It is a compelling narrative. It also highlights how we have funded everything around identity so far as side work for teams whose actual goals are elsewhere.
Right now:
HR owns data quality in theory but not in incentive structure.
IT owns provisioning but not the design of what good looks like.
Security owns policy but not the underlying systems.
App teams own their local admin roles but not cross system consistency.
When you try to run identity as a product in that environment, you end up with a roadmap nobody can execute because every backlog item lands on someone who has another manager, another set of KPIs, and another list of more urgent work.
For folks who have made identity a first class product, what changed? Did you centralize budget and headcount under one team?