One suggestion is that dissociation tends to develop when growing up around unreliable adults who are not safe attachment figures. The animals act as some kind of substitute and so friendships with animals will tend to remain important throughout life.
Another is that dissociative personality tend to me more prone to fantasy or vivid imaginations which create a more elaborate connection to animals or even objects (like stuffed toys) than might otherwise exist.
- Barlow MR, Cromer LD, Cron HP, Freyd JJ. Comparison of normative and diagnosed dissociation on attachment to companion animal and stuffed animals. Psychological Trauma Theory Practice and Policy 2012, 4, 501-506.