Am Freitag, 6. Oktober 2017 13:45:23 UTC+2 schrieb David Billington:

I don't know if it would save money as my understanding is you pay by
the weight of zinc added. It's a very effective bulk process and my
neighbour priced up galvanising versus painting in his former job at
Hanson and the galvanisingÂ* was cheaper and more effective, the paint
system if used would have required sandblasting the steelwork anyway.
The galvanising didn't require sandblasting but it may have been done
for extra protection, the initial acid dip removes any rust and mill
scale anyway.

Maybe it's just a way to save on the cost of the sandblasting to roughen the surface.