You can build this (story goes right):

      *   *   *   *   *   *
     / \ / \ / \ / \ / \ / \
    *   *   *   *   *   *   *-->*
     \ / \ / \ / \ / \ / \ /
      *   *   *   *   *   *

And obviously elaborate on it.

You can't build this (story goes down):

              *
             / \
            *   *
           /|  /|\
          / | * | \
         *  *   *  *--
        /|  |\  |\  \ \
       / |  | * * *  * *
      *  *  *

and so on and so on.

The problem is, no matter how you disguise it, gamers sense in the first case that they're on some sort of rails. Then companies promise the second, whether they mean to or not. But they can't deliver across one game. I remember thinking when I heard the announcement about the Mass Effect trilogy laughing at the idea that they could do it across three. You just can't let the combinatorics explode that much and make decisions that change the story. (Note things like "whether or not a Krogan squad is there" are consequences, yes, but you'll note they do not impact the future flow of the story, so they don't contribute to a combinatorial explosion. It's a linear contribution; you have to model the event and voice act it, etc., but it's still just two story nodes not significantly interacting with anything else.)

Fallout 1 & Fallout 2 were structured as several parallel instances of the first example, which is probably the best compromise you can make to prevent exponential explosion while still giving some heft to the choices.

But ultimately, if you want your "choices to matter", you'd better stick to "classic" roleplaying. A Dungeon Master can react to your unexpected choices and set you in a standard "fetch the thing" quest but then react to you actually accidentally literally destroying the world when that wasn't written into their "plan", and then carry on with the resulting consequences if you like. Computer games are still a long, long ways away from anything like this: https://www.youtube.com/watch?v=1H-1WJtuzPg