Science fiction in the United States has an unusually dense convention circuit, and it does professional work that other genres handle through agents and offices. Careers move through those rooms.
The genre grew out of organized fandom
Readers of the early magazines wrote to each other through letter columns, formed clubs, and began meeting in person. The convention is the institutional form that grew from those clubs.
Because the audience organized itself before the industry professionalized, the meeting places were never purely commercial events run for publishers.
That origin still shows in how conventions are structured, with volunteer committees, member voting and programming chosen by attendees rather than by exhibitors.
Editors are physically available
At most conventions the people who acquire novels and buy short fiction are on panels, in the bar and at readings, and they are approachable in a way that email does not replicate.
A writer can hear an editor describe what they are looking for, ask a question, and become a recognizable name before submitting anything.
None of this substitutes for the manuscript, but it changes how the manuscript is received, because a submission from someone remembered is opened sooner.
Panels function as public apprenticeship
Programming covers craft, publishing contracts, rights, self-publishing mechanics and the practical business of a writing life, taught by people currently doing it.
For a newer writer this is often the first exposure to how the industry actually operates, delivered by practitioners rather than through paid instruction.
The information travels back out through blogs and workshops, which is why the genre's working knowledge is unusually widely shared.
Awards are decided by the same community
Several of the field's major awards are voted by convention members rather than by juries, so attending, reading and voting are continuous with each other.
This ties recognition directly to the readership, and it makes the convention calendar part of the publishing calendar, since eligibility and ballots follow it.
Publishers plan releases and promotional pushes around those dates, treating the circuit as a distribution channel for attention.
The circuit also gates who gets in
Travel, hotel and membership costs are real, and a writer who cannot afford to appear regularly is outside a network that others use continuously.
Organizers and publishers have responded with grants, virtual programming and regional events, which spread access but do not fully replace being in the room.
The genre's openness and its barriers come from the same structure: a career advanced by presence rewards those who can be present.