As with every seemingly nonsensical internet phenomenon it has a deeper meaning. It is a hyper-masculinised imitation of the exact kind of reaction most people would have expected from animal rights activists. What's more it strikes a somewhat satirically racist tone with parallels drawn between harambe and the victims of police shootings in the USA, with the participants ironically acting the part of BLM.
All this is combined with the infamy of 2016 as "the year where lots of celebrities died", creating an atmosphere where online mourning on social media had become routine, even banal and frustrating. However with no other way to openly complain about genuine sadness, the aggressive parody in harambe-mourning became a much-needed outlet for those who were fatigued with online memorials.
Harambe himself was never the focus. Notice how any attempt to steer the joke away from insincere righteous anger and grave-weeping is met with tumbleweed.