IMHO one limiting factor is that games keep starting from scratch.
Devs keep trying to cater to practically blank slate gamers in aiming for the greatest available demographics. Every game has to be accessible enough to someone who never read the manual and possibly never looked at the tutorial (if present) either. So everything has to be shallow enough to be understood at a glance. Shooters must be simple enough to appeal to the CoD-MP or e-sports crowd, strategy games constantly re-hash the same mechanics and interfaces so nobody has to learn anything new, and every new iteration of a game must be made simpler so that more new players can be gained. There's just an infinite plateau of ever-the-same-rehash where high-end, high-complexity games for players who'd actually invest some effort ought to be.
It's understandable of course, especially financially. But I also think that there's some things to be said for catering to niche audiences; provided that they are still large and generous enough to support the devs.
But where devs actually put in more content, and dare to allow greater complexity, while also keeping things somewhat balanced and working, the really memorable games pop up. The ones you can read stories about, that keep surprising and challenging players. Dwarf Fortress, EVE Online, AI War, ArmA, Kerbal Space Program, Jagged Alliance 2.1.13 - there's some of these in every genre. They're naturally rare, enjoyed by relatively small crowds, and development on them is always a huge effort - and development mistakes resulting in a lower game quality tend to be more than likely.
But they also grow old and keep being played, because there's so much content and complexity. They grow old and things keep being added; not taken away for future iterations.
I know this probably once again puts me into opposition to Kasnavada, but I'll stick to my point: Catering to niche audiences that can stomach a steep and prolonged learning curve will probably result in more interesting and memorable games than trying to make simple games for everybody.
PS: It may well be said that complex, content-rich games are the native domain of modders rather than financially insecure devs. Probably true.
I'll agree with alot of this.
At the same time though, I also agree with Kasnavada's bit about games not absolutely having to meet those specifications to be truly memorable. It's just that the stuff you described seems to have a much higher chance of it. I can think of a good number of games that are actually quite simple and accessible, but are just utterly fantastic. And that's ME saying this, and I tend to just hate everything.
But yeah, I wish more devs would go a similar route of constantly adding content and complexity without warping the original concept. And if it has a tough learning curve, well, whatever, that's fine. The game in question is usually very worth it.
Though I think one of the biggest complaints from alot of people is "Well I just dont have TIME for that sort of game". That this sort of player will then pick up Generic Shooter #159347 and spend like 2000 hours on it doesnt stop them from saying that anyway. To me, it's more that they're used to having things handed to them on a silver platter, and dont want to bother with, you know, effort. I mean, once you get a handle on something like Dwarf Fortress or AI War, it's not like you NEED a 2 hour session with the game every time you play it in order to get some progress done. You can play for 20 minutes if you want, save and exit whenever you feel like it, and you'll have accomplished stuff, as is the nature of those games.
And just... ugh. Bugs the hell outta me.
I'm rather expecting that view to come from some people regarding THIS game too. It definitely already has a ton of stuff to it, and it's not finished. Even just the city stuff is complicated... the diplomacy stuff (or whatever you want to call it) sounds like it's gonna add alot more depth and sort of tie things together (which again is what I'm waiting for), but it's going to add even more complexity... and thus, more effort.
Granted, I can understand some of the frustration and confusion that goes along with learning something like this. It took me FOREVER to learn DF, and I"m pretty sure I watched through, what, *50* tutorial videos? AI War took quite awhile too. But once I got it down, it's all second nature, and it's easy to then keep learning more from that foundation. But still, that initial curve, more like a cliff, can be NASTY.
I forgot where else I was going with this.