Foundations

Why does my geotech report say piles when the building next door doesn't have them?

Because the building next door doesn't tell you much. You can't see its footings, and it may well have piles or deep footings you'd never know about. It also carries completely different loads, and ground conditions can change within a few metres: old fill, trenches, groundwater. "It's been fine for years" often just means nobody's measured it.

A lot of Melbourne, especially the north and west, sits on reactive clay that swells when wet and shrinks when dry, every season. A raft sitting directly on it moves with it. For something like a weighbridge, which has to stay level to weigh accurately, that movement means weighing errors, cracked concrete and failed verification.

Your geotech report is based on boreholes on your actual site, so it's the best information anyone has. Piles take the load down below the moving clay into stable ground. Sometimes there are alternatives, like a stiffened raft or replacing the reactive soil, but that has to come from proper design against the report, not from looking over the fence.