Many dogs move whenever their owner moves, including into bathrooms and along corridors that lead nowhere interesting. The behaviour has several distinct causes that look identical from the outside.
Group cohesion is the baseline
Dogs descend from animals that lived and travelled as a unit, where separation from the group carried real cost and staying with it required no justification.
Domestication then selected across thousands of years for animals that oriented towards people specifically, attending to human movement and position more closely than any other domestic species.
Following is therefore the default rather than a symptom. A dog that shadows an owner and then settles once the destination is reached is doing something entirely ordinary.
The reinforcement history nobody notices
Movement around a house predicts events that matter to a dog. Someone standing up has, across thousands of repetitions, preceded food, doors opening and walks.
Following costs nothing and occasionally pays. That intermittent payoff builds a durable habit far more effectively than a reliable one would.
Owners also reward the arrival without noticing, with a glance, a word or a hand dropped onto a head. Each of those is a small reinforcement delivered at exactly the right moment.
Breed background shapes the intensity
Dogs bred to work in close contact with a handler — herding and gundog types in particular — were selected for continuous orientation towards a person at distance.
Livestock guardians and some terrier types were bred to work independently and often show far less of this. The difference is a matter of working history rather than affection.
Knowing which end of that range a dog sits at helps set a realistic expectation of how much independent settling is achievable.
Separating attachment from distress
The distinguishing feature is not the following but what happens on arrival, and what happens when following is impossible.
A comfortable dog follows, lies down and disengages. A distressed dog remains standing, watches the door, cannot settle, and shows pacing, whining or drooling when a door closes between you.
Inability to be alone at all, rather than a preference for company, is the signal that professional behavioural help is warranted.
Sudden onset in an older dog
A dog that has always shadowed its owner is showing a trait. A dog that starts doing it in later life is showing a change, and changes carry more information.
New clinginess in an older dog can accompany declining vision or hearing, where a person becomes an easier reference point than the room. It also appears with pain and with cognitive decline.
A behavioural shift that arrives suddenly in a mature dog is worth raising with a veterinarian before it is treated as a training problem.