> "It breaks my heart that when this project was started in 2017, some 20 years after web accessibility advocacy had started in earnest, the developer was still uninformed enough about accessibility that they would create a custom button component with no ARIA support."
You're assuming ignorance and malice, when in all actuality this most likely comes down to priorities, and a painful lack of clear standards and tooling. By all means - please submit a patch with what you deem is the right solution here, instead of just expecting things get done your way on day one.
> "The buttons are clickable divs, not actual HTML buttons"
What's an "actual" HTML button we can all safely use to replace simple divs (which are just about the only way to get content to show up and behave uniformely across browsers and platforms, using as little js/css hacks as possible)?