I recognise a lot of the various scenarios painted here, and some are really "not on".
Yes, those "singarounds" where the host only asks people he/she knows personally to sing - harumph, the rest of us can sing too, you know!
And not getting a song when the last few before you choose to sing 40-verse ballads when they know time is running out.
And been at one of those where the host seemed compelled to ask the festival guest singers to sing 3 songs each before asking any of the "floor singers" to have a turn, with the result that many people in the room, all singers, did not get a song in a two-hour session. Yes, we love the professional singers, but they could be heard at the concerts that evening
The duos thing: My friend and I often go to festivals together: we are NOT a duo but 2 independent people: I sing a song, she might accompany me on her mandola. She would also like to sing, but how often is she passed over, unless we protest?
Then there are the self-appointed accompanists who try to pull people into a different key or rhythm, when they don't want to be accompanied at all. Or everyone with an instrument wades in full tilt and drowns out the poor singer. Or the people who accompany themselves on LOUD instruments, (concertinas, melodeons, accordions, even fiddles) and don't realise we can't make out a word of their song!
Talking during tunes: we once had a real standoff when this happened and the tune player rightly told the talker to shut up and listen: "you expect us to listen when you're singing, so why don't you listen when we are playing?"
Most of the sessions I go to, with a few notable exceptions are "mixed", so songs and tunes both happen: at the best organised one, the host/facilitator, will make sure that there is a balance of these, e.g. a couple of songs then a set of tunes, and so on.