This is addressed at the bottom. I don't know if this is true but the problem seems to be, although the posts show up chronologically in each thread, the threads might be out of order with respect to each other.

Depending on where you were connecting from, there could be serious delays in usenet. Like, some servers synced once a day kind of delays.

It's important to note though that hardware muscle and bandwidth were both much, much, much more scarce and expensive back then.