Fair that they were probably less ephemeral than I have them in my mental model. Which, as you guessed, was largely from them taking up the same spot as a slack (edit: I meant irc) instance in my mind. Slack, in particular, often had policies applied so that messages were deleted after a set time frame. I remember people complaining, but that seemed legit to me and fit my model.

I also confess this model of ephemeral conversation is amusing in this specific website. Which I also largely view as a clubhouse conversation that is also best viewed as ephemeral. But it is clearly held for far longer than that idea would lead me to think.