Because he's a spiteful tosser. Read one of his reviews and he called up the managing agents of a WG's flat and told them what was going on there just because he had a bad time with her. Obviously gets a kick out of these sorts of antics
And only 3 out of his 7 reviews are positive - but no wonder, since he seems to focus on the Romanians at 100/hour.
Also, only 2 of the 7 are still active on AW and one of those is obviously a replacement profile because his review of her (negative!) was in August 2015 and she is shown as joining AW 3 days ago.
Furthermore, he has so thoroughly explored AW that he knows who works with whom and where and includes it all in his reviews. With that many negative/neutral reviews one wonders whether he might be the cause.