I literally just had a dream about this. Where I needed to urgently send a message, but I kept messing up the text. Weird. At least now, I know I'm not just fat fingering it.
Hi, I've been making iOS apps for over 10 years now. I've experimented with many different styles, and even started doing android and web development. One thing I learned is that every abstraction or indirection makes things slightly harder to read and debug. Observers seem to have been a solution to 'callback hell' before async was a thing. However, it's rife with pitfalls.
With Observers:
We have hidden control-flow and lost intent. They subvert the readability of the developer's intention, in some cases they make you lose the callstack, and it has you searching the project on what code modifies a variable which is a lot harder than searching for a function call. Don't get me started on dealing with handling errors and out of order events. And oh man, is it easy to just avoid using encapsulation and creating a good interface/api for your piece of code.
Most of your code isn't re-usuable as you think:
A lot of things are naturally and forever tied together. Your UI is a reflection of _some_ model, The actions it can perform is based on it's current context, and if your UI changes then your business logic and model probably changes as well. This die hard need of separation and modularity only increases the complexity of the code with the majority of times the code not even being reused.
The only case that I've found somewhat reasonable to use observers is the database. What caused the database to change and effect it has is already pretty far removed from each other when a piece of UI needs to reflect the database.
Granted, It's possible to work around some of these issues, but please please I'm tired of debugging why a menu only opens 50% of the time because there is a piece of code several classes away from the context that doesn't fire correctly and looks like if (child.preferred.child.model.somethingElse.isFinished) { child.menu.child.openMenu = true }
Games are designed to be addictive, so once you stop its like quitting soda.. eventually you lose the taste for it.
Though, I noticed a lot of satisfaction from my life comes from interactions with others. Games no longer encourage quality interaction like they used to. Your friends get older then get married and get busy, so theres less of that. I usually analyze a game and decide if its wasting my time or improving my time on this earth.
Then there are the single player games. I feel like these had more meaning when the market wasn't as saturated. A lot of times you're just chasing nostalgia from that one really good game you've played. Hoping to recapture the same feeling. Not only that, most aaa games now days are now products of money instead of passion.
So if I had to guess why anyone stopped it's probably one of the reasons above.