They kept nothing but the name itself and a few cherry picked series' concepts [asset names], and where these were used, they were never like what the names originally meant.
This was wholesale exploitation of the reputation—to sell modern crap under the old name.
Exactly this. It's all calculated corporate brand exploitation and nostalgia-baiting.
A 2 second google search shows there's 2500-3500 miles between coasts. Not to mention it's in an apocalypse and transportation is quite rare, at least as of Fallout 3. In Fallout 3, the BoS walked from coast to coast, while most of them were wearing power armor. The Enclave flew to the east coast, which is more believable, but the Enclave was completely destroyed after Fallout 2. So how is the Enclave on the east coast if they're dead? And Harold is one man, a single, frail, old, man, yet he walked from Gecko(northern Nevada) all the way to Washington DC. In 30 years. In 80 years, all Harold went was from southern California to Northern Nevada, but 30 years later he made it to DC? Not to mention that he becomes a tree, which didn't start growing from him until around 160 years after the war, but 30 years later he is a tree.
A google search also shows this:
2161 - Fallout 1 begins
2241 - Fallout 2 begins
2254 - A Brotherhood of Steel squad led by Owyn Lyons is sent to Washington, D.C. on the East Coast to search for technology.
2277 - Fallout 3 begins
Here, Google is assuming a walking speed of about 3.05 miles per hour. Let's be generous and reduce the walking speed down to only 1 mile/hour; that's now 2,653 hours of travel time. If a walking group travels for 4 hours a day on average, they will reach their destination
after a mere 663 days, or 1.82 years.
You mentioned they were wearing Power Armor. So you can even reduce their speed even further and make them travel for an average of only 2 hours a day at a pace of only 1 MPH, and they will still arrive on the east coast after about
3 and a half years.
As for Harold...Let's say that he's frail, old, and took no transportation, so he travels for an average of 30 minutes a day, at a speed 0.5 mph. He could travel from Bakersfield (I know, he started in Gecko, but it's close enough) to D.C. in 10,612 days, or 29 years.
For the Enclave, some percentage of them somehow survived the events of Fallout 2 - maybe they were stationed elsewhere, or doing other things - and flew over to the East Coast in response to Eden's radio signal.
Given these time estimates - even if we slow them down further due to delays - it's not impossible for various factions to have made cross-country trips on foot. Yes, it is a great distance, but the human species has been known to use their legs to travel. It's how we spread all over the planet before recorded history.
Since this topic is supposed to be about Super Mutants, then it's possible for Super Mutants to have traveled on foot, too.