In our use case (and probably many others), we don't want users to see our CMS data models as editable because the data comes from elsewhere. However, we want users to be able to select that data to be used in a custom component.
Currently, if a model has "Hide From UI" selected, it doesn't show up in the models filter of the Content page and those models are hidden from the content list to the right. However, these models are also hidden from model reference fields in custom components. This means these models are locked down and unusable at the same time; they are just data in the application.
Allowing accessing these models from a reference field means you can add a bunch of data you don't want your users seeing or editing, such as product details synced from a CRM like Shopify, but that they can use in a custom component, such as a Product component.