Short answer: the spread is a price for liquidity, and liquidity is what disappears first around a scheduled release. It is not a fee your broker chooses to raise; it is what happens when the people quoting both sides step back.
What the spread actually is
The spread is the gap between the best price someone will buy from you at and the best price someone will sell to you at. You cross it on entry and again on exit, so it is a cost you pay twice on every trade regardless of the outcome.
In quiet conditions gold's spread is narrow enough to ignore for a strategy holding for days. In the seconds around a release it can multiply, and a strategy that enters at exactly those moments pays that multiple.
Why a release does this
Market makers quote both sides and profit from the spread. They can do that safely when they expect small moves. Facing a number nobody has seen, the same quote is a large one-sided risk - so they widen it, or stop quoting until the number is out.
Fewer quotes means a wider gap between the best two, and that gap IS the spread. It reflects genuine uncertainty rather than opportunism.
Why gold gets it worse
Gold reacts to the same US releases as the dollar, but trades in far larger nominal steps. The releases that empty the book are known months in advance, so the widening is not a surprise event - it is a scheduled one, on a calendar anybody can read.
The dates, and what our own record did on each of them, are on the news page.
How to see it rather than assume it
Spreads are broker-specific, so no page can tell you yours. Watch it on your own platform through one release: note it a few minutes before, at the print, and a few minutes after. That single observation is worth more than any published average.