Watching a gorilla group at close range or a leopard ignoring a vehicle is not luck. It is the product of a deliberate process that takes years and has to be actively maintained.
Habituation is the removal of a response
Wild animals treat an approaching human as a predator and respond by fleeing, hiding or displaying. Habituation is the gradual extinction of that response through repeated neutral exposure.
Researchers achieve it by being present at a predictable distance, behaving consistently, and never rewarding or punishing the animals' attention. Nothing good or bad follows from the human presence.
Done properly the animal reclassifies people as irrelevant background rather than as a threat or an opportunity, which is the state that allows observation without altering behaviour.
It is slow and species-specific
Great ape groups commonly take a couple of years of near-daily contact before they can be visited. Some species never habituate reliably at all.
The work has a cost while it is happening. Animals under early habituation are stressed, spend energy on vigilance, and may feed less, which is why the process is confined to a small number of groups.
That scarcity is the reason permits for such groups are limited and expensive. The supply is not the animal population but the number of groups that have completed the process.
Rules protect the state, not the animals' comfort
Fixed viewing distances, group size caps, time limits and prohibitions on eating or flash photography look like etiquette. They are the conditions under which habituation stays neutral.
Break the neutrality and the animals learn something new. Food produces begging and aggression, and sudden approaches reintroduce the threat response the process removed.
Illness rules exist for the same reason. Habituated apes have lost the distance that once protected them from human respiratory pathogens, so a common cold is a serious risk.
Habituation transfers to everyone
An animal that no longer fears researchers does not distinguish between researchers, tourists, farmers and poachers. The lost wariness applies to all people equally.
That makes habituated groups more vulnerable, which is why they are typically monitored daily and guarded, with the cost funded by the permits sold to visit them.
Where that funding or monitoring fails, habituation becomes a liability rather than an asset, and the group is more exposed than an unhabituated one would be.
The trade-off is deliberate
Conservation programmes accept the risk because habituated groups generate revenue and political support that unhabituated populations cannot.
The usual arrangement leaves most of a population entirely unhabituated and reserves a small number of groups for visits, which limits exposure while preserving income.
A visitor following the distance and time rules is not being managed for their own convenience. They are maintaining the conditions that keep the arrangement viable.