The only reasons that I've seen a site proposal being closed for are "not a viable proposal" and "duplicate." Are there other close reasons? What are they?
- duplicate of proposal
This proposal covers the same ground as another proposal. New proposals should define a new subject space not already being considered.
- duplicate of site
This subject is already well-covered by a live Stack Exchange site. We generally do not split off subjects simply to give them their own space.
- poorly defined
This proposal does not clearly state who might use the site, or what questions would be on-topic.
- content violation
This proposal has high potential to violate the Stack Exchange Content Policy.
- not a viable proposal
This proposal will not result in a useful, productive, or viable Q&A site.
- non-English community
Unfortunately, we are not currently accepting proposals localized to other languages — See Internationalization 'State of the Stack'. If this changes, we will post an announcement here.
1Obvious challenge: develop a proposal that qualifies for all six closure reasons at once.– MarkJul 7, 2018 at 1:26
A close reason not mentioned in the existing answer
This proposal covers the same ground as another proposal; it would tend to drain audience from another Stack Exchange site.
2You are citing the old description of the "duplicate of site" closure (updated description in my answer). The old description was changed awhile back because it often raised pedantic arguments that an unpopular (but still duplicate) subject would not meaningfully "drain audience from an existing site" because their diminutive size was of no consequence at all. Jul 17, 2018 at 19:35