I’m an old guy who knew usenet in its early days and IRC ;o)
In flat mode it is unreadable and in the end, few people read when it exceeds ten messages (except the people concerned) Too bad for the others.
The conversation mode, like Usenet, allows you to have a correct view of the entire discussion with the “disgressions”
Nothing prevents you from having flat and conversation mode. Everyone makes their choice
The only argument I understand is the size of the screen on a smartphone. But here, I think that the solution exists in other types of software
I stop here. I have the answer (old->2012). Thank you for pointing that out to me
Sincerely