Spirit forum was discussed frequently when Talkboard (TB) existed & reasons for why it didn't is in that forum (archived). Whether those reasons are still valid can be debated. Them being
#1 & some FTers flying them regularly is not the criteria for new forums
At one time in TB there was a sticky for criteria for new forums. Evidently that disappeared when the forum was closed/archived. Perhaps the mods in this forum can find it & post it here so some can put together their case for a Spirit forum.
Actually,
JDiver incorporated that info into the Welcome post in this forum.
Criteria here:
https://www.flyertalk.com/forum/27612638-post3.html
Cheers.