One possibility is sheer ignorance. We grow up in a society that builds an invisible wall between ourselves and wildlife, between "civilization" and "wilderness". For most of people, the only experience they have with wildlife is through mostly anthropomorphized culture such as story books and television/films, zoos where non-human animals are separated from humans by a safe barrier, and harmless creatures that are generally ignored such as city-dwelling birds, rodents, and insects. In a way, we draw a non-existent line between ourselves and other wildlife, a line that seems to come equipped with a protective bubble inflated by ignorance. And perhaps these tourists take that line with them when they venture out into the wilderness, seeing a bear or bison as harmless as the caricatures they grew up with, and likewise themselves harmless toward the dolphin and sea turtle they grab at like toys.
Another theory is based on something all of these situations seem to have in common. It is not just about the interaction, but about documenting and sharing that interaction. All these cases involve people posing for a photo. It is as if their need to show off - "Hey! Look at me! I'm practically touching a real-life bison! I'm so cool!" - overrides any consequences of their actions. Unbridled vanity and a need to flaunt it.
If I had to guess, I would say this behavior stems from a combination of these factors - obliviousness to the reality of the situation as well as vain attention-seeking aimed at upping oneself in social status. And I am not saying that we should not interact with wildlife at all - we are also animals who share this world too. But it is one thing for an animal to mutually interact with you and another thing to force your interaction onto it. Perhaps if we spent more time experiencing and observing real wilderness, as vulnerable as a fawn in the presence of a wolf, that invisible line may begin to fade with our ignorance and we may develop a healthy respect for the life we inhabit the world with.
TL;DR: Don't be stupid, respect wildlife.