they are a market place with most goods sold buy a third party. buy trainers from Nike, jeans from Levi, TV from Samsung, so on. or some shopfront for an independent shop, so they increase their reach from their town to the country or abroad. other than the stuff from China i dont find prices...
they're usually advertising using the railway.
its funny though seeing this arguement on this board, as BML did use to have a rare examples of competition, cheaper fares to London by Thameslink than Southern.
dont believe for a minute the ticket office staff have encyclopedic knowledge of the ticket options, might have some local hacks but for general tickets they just read off the computer. ticket machines give me the cheapest available option whenever i use them.
or, money gets taken as taxes to fund the free service. it may be the burden falls to smaller number of individuals, more benefiting from free travel, the net effect is less money available for spending elsewhere.