Three names get the call. The rest get nothing.
Someone's switchboard trips on a Sunday. They search "electrician near me" on their phone, and before a single website appears Google shows a map with three businesses. They ring the first one that looks legitimate and has reviews. If nobody answers, the second. It is rarely more considered than that.
Which three appear is not random and it is not only about distance. Google weighs how complete and specific your profile is, whether your primary category matches what was typed, whether your service areas cover the suburb they're in, and how many recent reviews you have.
Most Adelaide trades set up a listing years ago with a name and a phone number and never touched it since. That is genuinely the cheapest visibility available to you, sitting unused — and unlike ranking a website, it can move in weeks.