Finally to my point, The NASA crawler is on a near perfect path and despite this it will cease operation if it tilts 5 degrees or more in any direction, and it moves at 1.6 miles per hour. This clearly was useful pre-war for moving the repair, housing, and command facilities near the projects being worked on. It was a base utility at best, with no practical combat application.
Now Post-War with degraded road conditions, I doubt it could crawl a foot before hitting a 5 degree incline. Thus it would be fully immobile.
The BoS was left with the option of destroying it, finding enough people to staff TWO locations with five hours travel distance between them, or relocating from the Pentagon to Adams AFB in order to maintain a wing of vertibirds as there are no facilities for doing so at the Pentagon.
You may point out that last option as being viable and I can quickly quash it. Who won the battle of project purity and why? The BoS won because they had homefield advantage, and this was reinforced in the first hour of BoS when Liberty Prime was destroyed in transit to Adams AFB.
Why can't the BoS just get more people to staff it? Well that is answered by Ashur in the Pitt, he is ashamed he had to turn to the slavers to begin the reclamation of Pittsburgh. Ashur had flexible morals which lead him away from the same BoS who would be incapable of making the same choices. They are power-armored boy scouts, you know the "Good Guys".
The BoS are limited by their own morality, go back and listen to Ashur. Just like Lonesome road, it starts off weird and disconnected but as you become familiar with the wasteland it grows on you.
Not buying the 5 degrees tilt destroys it argument, since the Broken Steel Mobile Base Crawler clearly does not have a huge rocket or a space shuttle precariously sitting on top deck like the NASA crawler usually does/did - AFAIK this is what causes the tilt limitation really. Enclave mobile base crawler has more sturdily attached structures built on top, permanently welded into the platform, I have no doubt it could take more significant tilt and slightly worse path conditions - If it was so completely immobile, Enclave would not have bothered building their base on it, instead they would have gone with a more reinforced bunker with a satellite dish. (As a sidenote, I have also seen numbers mentioned, that without the rocket loaded, the NASA crawler can do like 2 miles an hour.)
Also worth considering is, Adams AFB propably was not the original home of the crawler (No vehicle assembly building can be seen around for one), it must have been driven there from somewhere else, somehow.
Even so, taking the Enclave Mobile Base Crawler somewhere would require advance planning and clearing a wide path for it from any large pieces of the post nuclear wreckage like pieces of fallen buildings, to prevent the tracks from getting stuck or thrown. Whole vehicle weighs something like around three thousand tons, with one individual segment of a track weighing in almost a ton - It can undoubtedly crush minor obstacles like frex automobiles into metal pancakes without slowing down at all.. Come to think of it, the main problem here really would be the workforce required - Dozens of techs to operate and maintain, lots of people with heavy equipment (robots or powerarmors perhaps) to plan and clear the path.
It would absolutely be worth it to acquire and move the crawler IF the Lyons Brotherhood could actually pull it off. Techies part would be easy for the BOS, their scribes could get this done no doubt, but the problem would be to get a hundred or so manual laborers with robots or powerarmors to clear the path, BOS might have difficulties with that one, not willing to employ any wastelanders ever and such lowly manual task might be seen as degrading and improper for their shiny knights and paladins; perhaps even using sentry bots for debris cleanup duties would be seen as a perverted use of a technology they hold sacred, who knows.
IMHO, the moral limitations here is not just about them being 'the good guys' but also having lots of attached technology hoarding and worshipping mindset baggage - Deep down, BOS considers technology and knowledge, especially advanced technology like lasers and powerarmors, more important than people, going as far as to consider some pre-war inventions as sacred, in their opinion too powerful for anyone outside the BOS to have.