 Why does Johnson stay on the asteroid, even though few people come by?
Characteristically, Harvey Ellsworth tried to maintain his dignity, though his parched tongue was almost hanging out. 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. In their hectic voyages from planet to planet, the pair of panacea purveyors had encountered the usual strange life-forms. 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. Medical science is unanimous in proclaiming this magic medicine the sole panacea in the entire history of therapeutics." "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. It's bitter as some kinds of sin before it's purified. "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.
 Here he's able to take advantage of travelers who are lost or in need of supplies.
 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.