@Andrew Hodges That explains it. Thanks for the quick reply!
I moved all the folders into the "General" directory, effectively making "General" the root directory.
I realized that in this case, we don't really need another Team channel besides the "General" channel, so I deleted the new Teams channel I had created, too.
I fell victim to the temptation to create "micro-channels" within a team, which I can already see is not necessarily the best way to do things. Too much fragmentation can be worse than not enough.