New Vegas sets up most of the main factions to die

I feel like I'm going insane because I've seen so many people get mad that New Vegas, the NCR, and Ceasers Legion got destroyed but that's pretty much the narrative end point of the game. Both Ceasers Legion and NCR are following China and USA's footsteps into the grave as they're both stuck in a ideological war that will/does end up in their mutually assured destruction. The battle of Hoover Dam replicates the shadow of war that the nukes represented and once both sides commit to the fight they've ensured they were going to be mutually destroyed.

Plus no one actually achieves their objectives to keep their factions alive by the end of the game. Even if NCR wins and holds the dam the campaign still ends in failure as the Mojave isn't the resource rich paradise that will repay all the caps and blood lost over the campaign. Because the rich gold mines by camp searchlight are now a irradiate hellhole along side the cottonwood cove mine. Nor is the Mojave a rich farmland as the sharecropper are barely eaking out a living even if you fix their water problems from whitewash and vault 34 plus the NCR currently doesn't have a food problem anyways as they predict it will take decades for their population to grow to a point where they would have problems. Nor is New Vegas actually a rich target for them as it's wealth came from the NCR itself. Hell even the costly repairs they did to hoover dam was all for nothing as the generators are exploded during the battle for hoover dam and there is no way they can afford to repair them again. All of this is on top of the locals resisting NCR rule as everyone from good springs to westside don't want them around and are on the edge of a rebellion. This is all symbolized though NCR hopefuls coming to New Vegas only to return back home broke.

Caesars Legion also was never going to survive because they never solved the problem of what to do when Caesars dies. Joshua Graham says it himself that no-one not Vulpis, Lanius, or even himself have the logistical mind the Calhoun has to keep the tribes together. That's without even considering the cult of personality that he built around himself is the knot that keeps all his tribes together but it's something his line of successors don't have. Plus it's literally a recreation of Rome, it's basically a national tradition to go into civil war.

Then you have Mr. House who is greed and hubris incarnate. He is so confident in himself and his algorithms to predict the future that he's blind to the actual world around him. He was so confident that he predicted the exact time the nukes would be dropped he let the platinum chip sit in Sunnyvale overnight instead of rushing it over to lucky 38. Instead he let it sit for a courier to deliver it in the morning a mistake that would cost him millions of caps, his health, and Vegas itself. Yet he still doesn't even consider that his predictions could go wrong again as he plans to create a private sector of industry and launch people into space. Hell he can barely believe that someone might violate their contract. Then you have that he's a control freak that can't actually control anything. Instead he's forced to rely on outside support to actually fulfill his goals though his tribes and his securitrons and literally every single one betrays him. To start with the human side you have the Tops as Benny was his right hand man yet he didn't predict him stabbing him in the back and stealing the platinum chip away from him. Then you have the Ultra-Luxe siding with the legion and cannibalizing people behind his back. Finally you have Gomorrah also siding with the legion with the promise that they will have the entirety of the strip to themselves. Yet Mr. House is powerless to stop them without the Courier intervening (who also can betray him) as the casinos are too entrenched in the strip politically, monetary, and militarily for Mr. House to root them out with his securitrons. Speaking of securitrons even those aren't firmly in his control. Yes-man is a mutating virus entrenched in his mainframe apart of every single securitron. A literal unkillable entity that he is unaware of (While it's just a theory I'm pretty sure that's why the securitrons are glitching about during the TV series as yes man probably tried to take over but we will have to see how it ends). Plus old world blues you have doctor 0 who also hacked Roberts securitrons to make them go insane. So Mr. House is also set up to fall symbolized though the game as everyone is preparing to stab him in the back and he's completely unable to stop it.

So every faction in New Vegas is set up so that after the end of the game they would all fall apart even if they got their factions ending as they all fall into following the same road as their predicessors (or I guess Mr. House not learning from his own mistakes) into the grave.

I didn't really have a good way to slide this in but how are you guys surprised that Novac is destroyed? Novac dies in all but one of their endings and in that ending they pretty much all die but the ghouls come back in the last minute to help them rebuild and fight off the NCR to remain independent.