It's like when people go off on weapons appearing phallic. Pretty sure it's just cause both are kinda engineered for similar things. Weapons either penetrate stuff or shoot stuff out. Dicks do both. Freud was dumb as hell, don't be Freud
Like, yeah, you can just spray sperm everywhere like fish do, but it's expensive and difficult and you don't get all the other benefits of human sex like building relationship bonds and having fun and sword fights with your buddies.