If you have trouble getting developer teams to create threat models, or to spend time on those threat models, then the solution is to make them accept the risk incurred from not having a threat model for the application.
The idea is not to be confrontational. Instead, stating that a feature has no threat model is a very pragmatic, focused, and objective statement.
The idea is that the developer team must accept that they don't have a threat model. The logic is to create a ticket that says there is no threat model, and the ticket will be closed when the threat model is created. Alternatively, if the developers and their management team don't want to spend the time creating a threat model, they must accept the risk of not having one.
This can be difficult to accept, but it's an important part of the exercise.
(from SecDevOps Risk Workflow book, please provide feedback as an GitHub issue)