Ed, is there some reason why radio amateurs cannot document their
complaints,
if they exist, to the FCC directly?

They can, if they are certain that they are documenting BPL and not another
source. It is possible to misidentify other sources as BPL, so having a
time-domain and frequency-domain analysis of the received signal will be an
important cross check.

73,
Ed Hare, W1RFI