I don't think a lot of it has anything to do with lighting even if RT were to make that bit easier to implement,although it does make me wonder whether VRAM is a consideration too(needing to load a new set of textures for destroyed items).However, Just Cause 3 and 4 incorporated destruction physics into an openworld years ago. Merely the fact a door can't even be destroyed,or the fact that NPC AI models have not improved,or the fact the same 10 voice actors are used,etc seems more like an obsession over making games look graphically pretty,and the rest has been utterly ignored. Also massive open worlds existed decades ago,and processing power has increased in size by huge amounts,as has core count. Even Cyberpunk 2077 is a mediocre RPG experience and outside the main quests it's still an empty world populated by copy paste NPCs,and I really hope the Modding community can fix that. Games such as GTA V might be technically obsolete but they seem to do certain things far better than newer games.
Bit easier? Try a lot quicker and easier.... Again, see above example, 26 minutes to get somewhat decent results for just "one" scene/frame and 1 light source..... now add all the frames/scenes and multiple light sources throughout the game and work out how much time that would have taken and metro ee is pretty linear/closed.... of course when devs are still working on raster version then the true benefits of this time saved won't be fully realised but that day is coming whether we like it or not.
Everything in the development world always comes down to timelines and budgeting, if something isn't achievable or not required for MVP, it won't make the cut.
Yes we have had open worlds or yonks but they all feel/look dead with the same copy and paste done throughout, first game that actually had an immersive game world for me was assassins creed unity. Cp 2077 also feels immersive and like the city is lived in. GTA 5 is good but it's not really as good as people make out, npcs are still dumb, they don't have sentient like behaviour like some think and they are also scripted/set on a path, I wouldn't say either cp 2077 or gta 5 npc is much different to each other, both have their pros and cons.