Nothing against bicycle touring, but while a bicycle may force slower travel, a bicycle is not necessary for it.
A person can road trip in their car, truck, or van [1] at a similar pace. The daily cost of gasoline will be fairly low...less than about $20 per day even for a motorhome driving California.
How a person travels is more a matter of time resources. At 300 miles a week, it will take ten weeks to go from coast to coast. Few people have that kind of free time.
And if you have ten weeks for travel, you will almost certainly have a life changing experience irrespective of travel mode.
[1] or upon a motorcycle, moped, or scooter.