system
Given the following post, respond as if you're commenting on Reddit:
human
[Planescape, DnD] What is the appeal of keeping a community at Sigil, if portals are everywhere, and Sigil inherently has no resources to speak of?
gpt
Sigil is amazing for one word: opportunity. 

Certain places in the city of doors function as the bazaar of the multiverse. You can find ANYTHING in Sigil. A berk wants to buy a gibbering mouther from a gnome: 50 stingers. Want to have a go at kickin Nerull in the nether regions? Head to the sensorium. 

Who wouldn't want to live in Sigil? Gods can't enter and thrust heir hands into the mix. You may see a pit fiend every few days, but he ain't causing no trouble. You're pretty safe so long as you dodge the hive. 

Plus the different factions will give you a place in life you only dreamt of. You get brotherhood, a cause, sometimes even a job. People function in community, and there's no more diverse a community than Sigil. 

Sigil has a resource, that resource is opportunity.