Part of it is cultural. Far Cry 2 is from that time early on ps360 gen where "gritty realism" wad all the rage. People remember thr piss filter well, but there was more to it: moody atmosphere, perpetual hdlf overcast sunsets everywhere, over realistic violence, and dynamic physics. Half Life 2 had been released recently putting physics on the radar for everyone. FC1 sold people on the more versatyle big engines such as Crytek's. And doom sold people on highly dynamic lighting. All trends seemed to point to a future highly simulated games. Program real life and the game builds itself, seemed to be the idea. Cell was tounted as the next big thing. The 360 didn't have a weak cpu either. There was a strong focus on physics back then, which now has lost some of the hype. Devs were experimenting a lot back than. And many of those experimental games floped. Remember the Splinte Cell convicion prototype that was canned? Or the Alone in the Dark Reboot? And that Euphoria driven Indiana Jones game that never saw the light of day? FC2 was not very succesful either. Even GTAIV was criticized for loosing some of the fun in its apriach to a more down to earth world. Not only did the hype on physics eventually die off, but devs got tired of trying to make them work as expected and fail so often. More directed, pragmatic solutions became popular again.
GTAV, FC3/4/5 and a couple other recent games are part of another new trend. One that is exactly the reaction to the "gritty realism" one. Games that are not trying to be realistic, but rather like a Hollywood Action Blockbuster. Like HL2 FC1 and Doom helped pave the way to that style back then, Uncharted and COD did it for this one. It's all about fun. The industry settled to more tried and true production techniches to try and restore some sanity into the extremely risky endeavor that is AAA game creation, which did bankrupt so many studios and publishers on the early ps360 days...
Sistemic worlds are not entirely dead though. But they are not coming so much on the form of procedural physics and animation, but through other elements of game design. Games are more and more open, levels more broad and experimentation-inviting. Missions have become less directed. All big titles have their share of RPG elements, and even Japanese studios who seemed to be behind the curve on this push for simulation-based open world sandbox games caught up with MGSV, FFXV and Zelda BoTW..