Idk tbh. It's just how they wanna display it. I personally think it's fine how they're doing it but I do see your point in having it as a progress bar/percentage but the only thing I can think of that could be an issue with a progress bar/percentage is that it might not be as easy to put into an estimation, how much code there will be. Plus, if there ends up being more than expected, then the time between progress updates potentially becomes less frequent and consistent. Obviously it would be nice to have an overall idea as to how close to the finished product they are but it just might not be that easy.
Either way, I think the current system works fine. It's not perfect but it works.
Sorry if I still didn't quite understand (I'm a lil slow sometimes XD) but this is how I interpreted how I should reply. :))