Why are some properties not animatable or driver-able? (TextCurve.body)

I’m making a little Unit Circle animation using Grease Pencil, Hooks, and Drivers. (Just to learn the tools, honestly.)

I got a basic scene working, and I’d like to add some labels (theta angle, values of the trig functions at theta) to it. I thought I could just manipulate a Text object’s internal text with a Driver, but the body property is not animatable. Apparently there are ways of animating it, but it’s python-hackery at best and I’d prefer a different solution if at all possible.

Finishing off, I’ve got two questions:
Is there a better way?
Why isn’t this property animatable?