Consider "likely" suspects:
* Conservatives like us'ns - we find DU highly entertaining, so we wouldn't hack DU;
* Trump & Trumplings - they see DU as making Libs & Progs look bat-guano insane, and wouldn't interfere with that;
* Russian hackers (if any of the sort DU hates actually exist) - DU advertises their successes (if any) and prowess (real or fantasy), so they wouldn't stop DU;
* The R Party - they see DU as making Libs & Progs look bat-guano insane, etc.;
* The D Party - they see DU as making Ds look bat-guano insane, an image the D would gladly shed;
* Clinton operatives - punishment for failure;
* Bernie operatives - revenge for supporting
The CHILL and for driving out the
Berniebots;
* Skinner & Co. - give the overheated DU-loons a brief time-out and divert DU-folks' attention outward to an external enemy (Can you say, "Reichstag Fire"? I Gotta obey Godwin's Law,

).
IMO, the only parties with significant motives (other than boredom relief) to harass and shut down DU are Libs & Progs.