Honestly? I'd argue the world ending in nuclear fire was the best possible outcome for the situation Fallout's world found itself in.
Fossil Fuels weren't scarce...they were effectively gone. Oil, Coal, Natural Gas...what was in production was all there was ever going to be and the US was in control of the world's last remaining oil field. China invaded Alaska to get at that oil, just as the US invaded and annexed Canada to secure a Pipeline access route. China was developing stealth technology, the US was experimenting with viral weaponry.
Thought I was going to say Power Armor? That was the practical side of things, really. Imagine how many suits of power armor you can crank out to make each Infantry Man a walking tank vs producing a single tank? Even the most iconic of Fallout's armors is a direct result of the resource crunch the world found itself under.
But the US was worried about China developing bio-weapons, so they started dabbling in that themselves to create a universal antidote...and ended up with the FEV. They already had Deathclaws pre-war and Fallout 76 confirms Super Mutants were a known outcome as well. Had the world not burned, imagine the horrors that would have been unleashed by FEV. The Deathclaw is the most feared predator in the Wastelands for good reason, and that's the only known Military FEV bioweapon. That was the FEV's "alpha stage".
As for the Enclave...they were one group among many pulling the strings. Vault-Tec had its own, equally mysterious agenda. Space Travel in Fallout becomes problematic when the Zetans have been an acknowledged facet of the universe. While I do consider Mothership Zeta to be akin to the Guardian of Forever segment in Fallout 2 (In which the Chosen One, transported into Vault 13 in the past, ends up breaking the water chip that directly leads to Fallout 1), it's heavily implied that it was the Zetans who extracted the nuclear launch codes that kickstarted Armageddon. FEV could play a big part of that.
Ultimately, the motivations that lead to the end of the world are irrelevant. What I feel needs to happen with the franchise is a move forward, to see what the world after the bombs ends up being. And that's something Bethesda isn't doing a very good job at, since right now the West Coast of the United States is starting to become civilized after a fashion, but the East Coasters are still picking through the dirt and refuse of the old world. The Tribals of Zion National Park have more culture than the average Commonwealth Waster.