I'm not trying to be argumentative either; it's difficult to communicate about physicality fully in this medium.
If I am throwing into a backwards fall correctly, I will have locked my partners spine and cause their feet to suddenly thrust forward (as if stepping upon a roller skate). Either one foot or both feet. The fall that results will not be a back roll.
The only time that back rolls seem to work in technique is when uke chooses to go before the terminal point in their posture where their spine is still not locked and they can still take a step forwards or backwards.
In our system, if you can move like this as uke, you should not fall, you should take sente and reverse the technique, unless you're in kata training and you then wait for tori to figure out how to lock your spine and pin your feet to the ground or eventually recover to show tori that they missed the window for the technique depending upon where they are in their learning process.
Does that help explicate what I mean?
I think I understand. This probably indicates mostly style differences caused by choice of techniques and methods. Straight down throws are generally hard to roll from - I tend to roll systema-style sideways and down across the shoulders for those situations - but that takes practice and agility. Most folks would just take a breakfall and roll sideways or try to kick/trip the opponent (in a confrontation).
If all of your *real* techniques are straight down throws from a locked position (nothing wrong with that at all), I can see where backward rolls would seem hard to execute and not worth trouble to practice that often.
In a confrontation though, you can get knocked over and pulled down in awkward non-technical ways, that would merit having a backward roll available in the toolbox. And certainly there are definitely non-budo reasons for having the backward roll in your toolkit.