An elephant that will tolerate a vehicle at short distance will react strongly to a person on foot at several times that range. The difference is in how the animal categorises what it sees.
The vehicle reads as one shape
Wildlife habituated to game drives perceive an occupied vehicle as a single large, predictable object with a consistent outline and sound.
Humans standing separately register as individual bipedal animals, which most large mammals treat as a distinct and more concerning category.
This is why guides insist that everyone stays seated and inside the outline. Standing up changes the silhouette and can convert a relaxed animal into an alert one immediately.
Habituation is learned, not natural
Animals in long-established reserves have encountered vehicles repeatedly without consequence, and the neutral association builds over generations.
The same species in areas where vehicles are associated with hunting or harassment behave completely differently, fleeing at distances of hundreds of metres.
Habituation is also specific. Animals may accept vehicles while remaining highly reactive to people on foot, because the two have never been the same experience.
Predictability matters more than distance
Approach technique determines the outcome more than the final gap. Slow, indirect approaches with stops allow the animal to assess and continue what it was doing.
Fast, direct approaches read as pursuit, and once an animal has moved away because of a vehicle, the sighting is over for everyone.
Engine handling follows the same logic. A constant idle is less disruptive than repeated starting and stopping, which is why vehicles often sit running at a sighting.
Walking safaris work from different rules
On foot, guides deliberately maintain distance, use wind direction and terrain, and approach so that animals are aware of people early rather than surprised.
Surprise at close range is the central risk, particularly with buffalo, elephant and hippo, so the technique is built around avoiding it.
The experience differs accordingly. Walking delivers fewer close large-mammal sightings and far more of the smaller detail that a vehicle passes at speed.
Habituation carries a management cost
Animals that ignore vehicles are easier to view but also easier for poachers to approach, which is a documented problem for rhino in particular.
Heavily viewed predators can also be displaced from kills or interrupted during hunts when several vehicles converge, which is why reserves cap numbers per sighting.
The tolerance that makes viewing possible is therefore a resource that can be depleted, and the rules around approach exist to protect it.