question:  Why does Johnson stay on the asteroid, even though few people come by?
context: When Harvey staggered pontifically into the battered metalloy saloon—the only one on Planetoid 42—his tall, gangling partner was already stumbling out, mouthing something incoherent. Paying no attention to them, it was carrying a case of liquor in two hands, six siphons in two others, and a broom and dustpan in the remaining pair. The interplanetary con-men drank noisily, asked for more, until they had drunk eight glasses. "Out of Mars for Ganymede. Our condenser broke down, and we've gone without water for five ghastly days." He came near starving and moved on to Titan. "On account of the quantity, I'm able to quote a bargain price. The planetoid man worked the pump while the mayor intently watched the crude level-gauge, crying "Stop!" when it registered the proper amount. Then Johnson rubbed his thumb on his index finger and wetted his lips expectantly. After giving them directions that would take them to the free-water pool, the ponderous factotum of Planetoid 42 shook hands and headed back to the saloon. "Johnson, as I saw instantly, is the victim of a difficult environment, and must charge accordingly." In the fragile forest, they soon came across a stream that sprang from the igneous soil and splashed into the small pond whose contents, according to the mayor, was theirs for the asking. It was on the sixth trip that Joe caught a glimpse of Jupiter-shine on a bright surface off to the left. He uses only one pool, the sweet one! Him and me are the whole Earthman population of Johnson City." Johnson's eight-foot son, topped by a massive roof of sun-bleached hair and held up by a foundation that seemed immovable, had obviously been born and raised in low gravity. Harvey studied it worriedly, put his own hand somewhere on it, swallowed as it closed, then breathed again when his fingers were released in five units instead of a single compressed one.
output:  Here he's able to take advantage of travelers who are lost or in need of supplies.
options:  Here he's able to meet traders like Harvey and Joe and barter with them.  He's able to run business even with few customers.  Here he's able to take advantage of travelers who are lost or in need of supplies.  He doesn't want to give up the spring of water.