 Why don't the Altairians leave Altair I if it is so overpopulated?
He drew his carefully tailored Terran-styled jacket closer about his shoulders, shivering as his eyes avoided the black, yawning cell-holes they were passing. Interplanetary ruling. I mean, all they had to do was get a man over here, get the extradition papers signed, and provide transportation off the planet for me. I've got three million credits sitting in the Terran Consulate on Altair V, just waiting for me to walk in and pick them up. You walk into a newly opened planet with your smart little bag of tricks, walk in here with a shaky passport and no permit, with no knowledge of the natives outside of two paragraphs of inaccuracies in the Explorer's Guide, and even then you're not content to come in and sell something legitimate, something the natives might conceivably be able to use. No, nothing so simple for you. The Altairians are sore about it. And the Terran Consulate isn't willing to sell all the trading possibilities here down the river just to get you out of a mess. "You've committed the most heinous crime these creatures can imagine, and they're going to get you for it if it's the last thing they do. Trading brought scalpers; it was almost inevitable that where rich and unexploited trading ground was uncovered, it would first fall prey to the fast-trading boys. They spread out from Terra with the first wave of exploration—the slick, fast-talking con-men who could work new territories unfettered by the legal restrictions that soon closed down the more established planets. The first men in were the richest out, and through some curious quirk of the Terrestrial mind, they knew they could count on Terran protection, however crooked and underhand their methods. Altair I had been recognized at once by the Trading Commission as a commercial prize of tremendous value, but early reports had warned of the danger of wildcat trading on the little, musty, jungle-like planet with its shaggy, three-eyed inhabitants—warned specifically against the confidence tactics so frequently used—but there was always somebody, Meyerhoff reflected sourly, who just didn't get the word. They wanted land—this gooey, slimy swamp they call 'farm land.' "If you hadn't been so greedy, you'd have found out what a chunk of land was to these natives before you started peddling it. You'd have found out that they're marsupials, and that two out of five of them get thrown out of their mother's pouch before they're old enough to survive.
 They don't leave because they can only eat food grown on Altair I.
 They don't leave because they can only eat food grown on Altair I.  The Goddess won't let them leave.  They don't leave because no other planets will clear ships from Altair I for landing. Nobody likes liars.  They don't leave because they have not achieved space travel.