The shape of the breed
The Malinois is a medium-sized, athletic herding breed that was never designed to be a pet. Its working characteristics — speed, sensitivity, a high tolerance for repetition and a strong desire to engage — make it exceptionally trainable in the right hands.
Those same characteristics make it a poor fit for a household that wants a dog to be self-sufficient. This is a breed that requires a job, or something that functions like one.
Why it dominates the field
Practical reasons explain most of it: size, speed, stamina and availability. The breed is also unusually responsive to precise handling, which makes it rewarding for trainers who like detail.
Cultural reasons matter too. Once a breed becomes the visible standard in a discipline, it attracts the people who want to be visible in that discipline, and the cycle reinforces itself.
Where it goes wrong
The common failure is not aggression. It is anxiety produced by inconsistency — unclear rules, unpredictable corrections, and long stretches of nothing followed by intense demands.
Because the breed is so responsive, mistakes show up quickly and look dramatic. The dog gets described as difficult. Usually the dog is describing the training accurately.
A Malinois will not fill in the gaps for you. Whatever you leave out, it will invent.
Choosing one
Anyone considering a Malinois should spend real time with adults of the type they are thinking about, and talk to people who have kept them for a decade rather than a season.
Ask what the dog is like at rest. If nobody can answer that question, it is worth asking why.