As you’ll know if you’ve either read my first book or hung out with barbershoppers for more than five minutes, barbershoppers do like tags.* They like to sing them all night as a social activity, and when they have to sit in an audience and keep quiet, they like the people on stage to sing them for them. Hearing a someone nail a good long post and some serious chord worship gives a particular style of vicarious pleasure that is amplified by all the hours spent in stairwells attempting it yourself.
This is, I suspect, the reason why the genre has developed the phenomenon of the ‘out of context tag’. The arrangement charts its way through the journey of the song, and just as it is heading into where it should culminate, it suddenly dives off into a screaming tag from nowhere. An outsider might think: why would you do that? But an insider knows they do it because the other insiders in the audience will respond with delight.