You have hit on one of the longest running "Why's" in the PTC saga. In my, close to 27, years on this software, "why's" have existed with Pro.
I could spend the entire day reflecting and writing all them, but it would be of no value. I am sorry to say that I do not know WHY the note tab is grayed out for a simple hole. It would seem logical to have something like this at your fingertips. Why, you ask? I envision a scenario like this: while the hole tool was being developed years ago, someone asked, should the note tab be visible and useable in Simple Hole. The answer was probably "Heck no Goober, it's just a hole. It's just a round feature that will have a shown dimension available on the drawing. What more do those CAD Monkies need?". While thatmight bea good answer from a text book standpoint...I.E. a non-working, green engineer that assumes it's all easy on shop floor. Not always the case, Mr. Graduate Engineer.
What if one needed to specify running a de-burring tool on that Simple hole, or to mark the hole with paint? That embedded note seems really useful and nice to have it all in one tool. Maybe that makes too much sense.
But, then again.....if they didn't want the Note to be used, then WHY is the tab still there in the first place? Why?????