I'm having the same/similar issue - I can only get Tooltips to appear on editable fields.
It's important for our users with read-only access to be able see the tooltips to help them understand the data sources, calculations, etc. We'd prefer to use Tooltips instead of Hints to reduce visual clutter.
I've attached screenshots showing an editable attribute with a Tooltip, and a read-only attribute with none, along with one example of the how the tooltips were added (in the Project object, Views tab, selecting Fields, then the properties of the attributes that need tooltips.
We're on 14.4.