Discourse does provide a way to add image descriptions. Just because you don’t like the implementation does not mean that we are not leading! 
If you want to have a different implementation, then you are welcome to implement it as a theme component or pay someone in Marketplace to do it. If it works better than what we have now then it will be added to core. This is how alot of improvements end up in core.
That said, as part of the new composer work we are going to have to revisit this area of the UI. It’s on the list.