Maybe different service patterns, too: different volumes of different kinds of things to different kinds of customers. There's no export grain or coal or whatever coming to Boston via CSX.
If the Class One railroads were in fact keeping their trains to schedule, then running a few 500-foot passenger trains each day would consume practically no track capacity at all and cause no disruption and limited need for infrastructure improvements. But when you operate on a model that cannot anticipate when a 15,000-foot train may arrive/depart Mobile, AL (or any other terminal), then such scheduled trains - as minuscule and fleet as they might be - create a problem. It is a sad day when a highly profitable railroad that only runs 11 trains a day on a mainline can demand $2.3 billion from the taxpayers for infrastructure improvements to add a handful of passenger trains on a route of 145 miles. (Note: This $2.3 billion figure is more than CSX spent on capital improvements to its entire network of 21,00 miles in 2017!)