True, but apparently LE needs to make sure any "private" key cannot be used to issue a certificate if they are made aware of it. So true, the key isn't really private, but it's good practice to just not post it and it seems to be a hassle for the LE staff if posted here 
@JamesLE FYI, I've revoked (using keycompromise) 8 private keys from the Community by searching for the private key headers (RSA/EC) which resulted in 11 valid private keys of which 1 had an invalid EC curve and 2 were already marked as forbidden. So in total 8 keys remaining which are now marked as forbidden too 
Was a fun exercise in some Python and bash scripting Note that I let Discourse do the searching, so not sure if I got everything of course