I can't really agree with this. There are tons of great written games and they aren't as rare as you think. I love Bloodborne and Dark Souls is quite decent. The plot however is very sloppy and non-existent in my opinion. The game was made for gameplay purposes only and the story is dabbed in like pin-up notes. I would say the story is about as deep as your average Super Mario game. I've said it once and I'll say it again! I love Bloodborne and have hours logged in. I'm STILL playing it! ^.^ Elder Scrolls is another bad example because its story is like Zelda (but debatably weaker). Something to keep the gamer going but so bare boned that it can focus on gameplay mechanics.
I would use examples like Naughty Dog games for an example of fantastic writing. When you play their games for a second time you actually realize that their huge plot twists and major revelations were actually seeded in the game and even have hints that are unavoidable to notice once you know them.
I could make a huge list of well written games and it's been getting better and better. There are tons of old games with great plots as well, granted not as many! However there were still TONS that existed! :)
