It doesn't
but since they serve a similar purpose for many people I think its an interesting data point.
Discussion
It's interesting for a measure of "true" usd appreciation if you subscribe to theory of gold being best measure of usd inflation, sure
I don't think I subscribe to that one.
I think USD is a broken measurement and it's therefore impossible to have accurate pricing.
which is why I am so pedantic about maxis thinking a X/BTC chart is somehow informative of something more than degen gambling.