Pre-determined branching dialog was never a particularly good thing, but it has now been pretty much entrenched by the move towards spoken cinematic presentation. I agree it can get quite tedious when it's taken too far, unless that's what you are really like, just as too much combat is tedious.
How does one avoid pre-determined dialogue in a videogame, if I might ask?
Constructed on the fly from game context ( who you are talking to, what they might know about, diffusion of game event information etc ), conversation rules, and player input.
Developing a sophisticated conversation engine is non-trivial, even without voiced characters. If you want fully voiced conversations, you would have to also develop a voice synthesis engine, and add mechanisms to cater for spoken intonation, emphasis, volume, tone etc).
It's a lot easier for developers to not think about it, and just continue to use dialog trees, particularly for strongly scripted and cinematic games, which is the general trend.
I'm sure someone will eventually be brave enough to try something different.
