The idea is that the hint text (like "choose a product from the dropdown") and the default value the component will have, should be independent of the model it is bound to. This simplifies providing such a value and better supports view-model scenarios where the validation happens in the view-model and the actual model may not even be able to take the same values, because it relies on app logic to protect it.

The most obvious example is a required field - it must be nullable so required validation works, but the actual model may have to be non-nullable.