In my opinion, these two factions are so focused on the past that they are unwilling to create a better future.
The thought began to occur once I was reading through the entries in this wiki.
It's kind of tragic really, because both these organizations kind of started with good intentions at heart you know.
Enclave wanted to restore the country and the Brotherhood of Steel wanted to prevent technology from falling into the wrong and incapable hands. But they kind of lost their noble intentions to a struggle of dominance.
I actually feel bad for these guys that they are so living in the past that they are unwilling to work with rising powers like the NCR to build a better future.
It seems that the only right way to do it is like how the Followers of The Apocalypse try to.