Why is ID adding aria-labels to my Reflowable EPUBs?

It never hurts to have a suspenders-and-belt-and-safety-pin approach, especially in the wild world of EPUB. But at a certain point you have to relax to the fact that there are so many readers in play that no document, other than perhaps the very simplest one, is going to render optimally on all or even most of them. I choose to optimize for Kindle as one fork (which for all its faults is at least consistent across all but a few older devices), and then for Calibre as a baseline EPUB. Anyone using another reader, especially browser-based or OS generic ones, gets what they get. As with PDF, the burden of using a full-featured, standards-compliant reader has to be on the end user.

With InDesign plus CSS, you can create optimized EPUB exports that can be updated and replicated endlessly, without the tedious every-iteration editing of the exported file. I find that a worthwhile path.