I do find this odd, purely my own observation over many years of mailing lists, having been a list owner of several under rootsweb and currently under groups.io and having been a subscriber to many more on a variety of subjects, I can almost name the few who bottom post or reply with interspersed comments
Bottom posting is by far the most annoying, interspersed replies are okay once but once that is again replied to it loses any meaning
The norm for many years has been to top post leaving just enough of the message you are replying to, to keep the reply in context
Nivard Ovington in Cornwall (UK)
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The most you can do if you are the owner of the group, is to ban TOFU/top-posting and insist that members use the proper "old-fashioned" interspersing-method.
groetjes/?is, Ronaldo