Still comes across as very shouty and opinionated eg ‘it’s just mind blowing’ and ‘with this blatantly obvious chronic issue’, but let me try and answer you.
I am just a moderator here, and not a bbpress author. I don’t get paid anything to do this, and I’m just a guy sat in his kitchen trying to help others.
So a bit of background
bbpress was written by the founder of WordPress Matt Mullenweg as a standalone product way before mobiles/cell phones did anything more than phone and text.
It was added as a plugin to WordPress by John James Jacoby, who has done updates to it every so often as paid work by the WordPress foundation.
It is up to the owners of plugins as to how much work they do on their products.
The authors tend to release updates every few years, rather than more frequently.
My personal view is that you should consider bbpress to be a ‘mature’ product, ie any releases will be to fix issues rather than add functionality.
bbPress is used by WordPress on their support forums, and if you look at these, you will see that they show these columns in mobile, so that is clearly how WordPress wants it to work.
That you might decide that this is not how they should show is your opinion, and with over 100,000 installations of bbpress I have not noticed over the 10 years I have been doing support here ‘a lot’ of requests. I’m sure there have been some.
The bbpress concept is ‘We’re keeping things as small and light as possible while still allowing for great add-on features through WordPress’s extensive plugin system.’ This does have an implicit expectation that others will either have the code and css capabilities to change bbpress to suit themselves, or hope that others have done so through plugins.
You seem to have found some answers, and say you have found one that does this with css, and I suspect I might have answered some doing exactly this.
I do not plan to start from scratch, so maybe if you can give me a link to ‘there’s some people that use CSS but I haven’t seen where it actually works’, then I’ll see if I can help further.