Truth! Completely agree with your opinion here. A lot of story, especially dialogues, have become cookie cutter for sure. Now it might be because of the amount of games coming out too. And like you said, it could be because we are getting old, and the young don't care as much. But I go back into my teens and early twenties, and I used to play those 2.5D solve a mystery games with four five options to choose from. There were star trek ones, and some around detectives investigating the occult (I used to love these series but forget it's name) The dialogues in those were not Oscar winning but good enough that we forgave the blocky pixel UI and the story played in our head as much as it did on the screen. When playin games like Arkham Asylum or City, or even open ended games like GTA, that same compulsion to know what happens next, or interest in how things resolve is no longer there.
Having said all the above I did download a anniversary version of an old fav that we used to find hilarious when young - the Lounge Lizard Larry series - with its xrated jokes and scenarios in cartoon without any actual xrated scenes. Despite the cheap and cliched dialogues I remember finding the story and dialogues quite entertaining. Sadly it has not aged well and when i tried playing again it just did not have the same impact. So it might just be me getting old and jaded :D