I understand the arguments so far, but there is still something I
don't understand.

First, lets remember what was written, in the leaflet of qep'a' 2017:

"Finally... a note about -Qo'. There's apparently been some confusion
about -be' and -Qo' in imperatives. This is no doubt because this was
not explained as clearly as it could have been in the Dictionary.
The rule says -Qo' "is used in imperatives" and that -Qo' is "the
imperative counterpart to -be'." The rule isn't that -be' can't appear
anywhere in an imperative construction; it's that -be' can't be used
to mean "don't!" - use -Qo' for that. In other words, -Qo' is used
(and -be' is not) to indicate a negative command, when the meaning of
the command is "don't do X!" X may contain a -be', but if the command
is to not do X, you still need -Qo' at the end (if you're saying
"don't do X" and not "do not-X")".

(I copied the above by hand from the leaflet, so double-check with it
for possible errors).