mass effect has failsafes to ensure you can't get everyone killed until the final mission so you have a crew. sheperd can even die in the end of mass effect 2 and it'll still lead to an ending and game clear. This game could've done something similar where a few characters are necessary for the plot until they aren't. there's actually another game being developed right now by another circle kuronekogun that's going to play the way we wish this would though admittedly it's only 4 heroines. We've also got games like Leane 2 where everyone besides the MC is disposable
While what you're describing can absolutely be done, it's pretty clear that you're failing to understand what that means in terms of game development...
The fact of the matter is that every single choice of any kind that has meaningful impact on a game's direction and story automatically means writing a second branch of the story that takes this into account. Depending on the impact and complexity of the story, this can easily mean needing to wrote two separate stories entirely to account for the divergence, especially if we're talking about the presence of a character who's active in the plot. If you want things to make any kind of sense, you have to account for both how the other characters react to the loss, and how the enemy reacts to the win, etc.
The more characters and branches you get, the more writing you have to do, to the point where instead of a single story thread, you end up with a complex web of writing that's easy to trip up on.
But it gets worse. Story writing is much like drawing a singular image. How often do you see an image made by different artists at the same time? Not that often do you? Why. Because different art-styles clash, and the same happens with different writing styles. It's theoretically easier for different writers to work together, but not by that much, and the end result is that you still absolutely need a lead writer that organizes everything together and smooths out any tonal shifts and whatnot that show up.
Can it be done? Yes, but it adds a TON of time to things unless you want the story to implode in plot-holes. That's leaving aside the fact that the easiest solution to this conundrum is to just make characters less meaningful, which in turn makes their loss less important.
Mass Effect... and pretty much every Bioware RPG and plenty of other RPGs, pull this off by centering the story around a main character. At the end of the day, the story is all about Shepard in the Main Game, and all the real choices belong to Shepard. It's not just a matter of losing characters, it's also a matter of recruiting them in the first place. Even then, the fact of the matter is that the impact of each character is relatively minor if you look at it closely, outside of the ending events... Yet even with this bit of simplification, the amount of work they had to put in every bit of dialog is absolutely enormous to take into account all of the absurd variations that the game offers you.
TL;DR:
It ain't that simple, captain, and you should try something like that yourself for a bit, even as a mental exercise, before complaining so much.
Quite frankly, I very much doubt that No Future can afford the extra long development time it'd take to write in the level of complexity you're suggesting... and that's not even mentioning the nightmares involved in balancing and dealing with the end result on the gameplay level...
