Buyers need sellers

Liquidity matters because of one rule that has never changed. Nothing is bought unless something is sold.

Every buy has a seller

You cannot buy gold unless someone is selling gold at that moment, at that price. Your order is matched against theirs.

This used to be done on paper by hand. Now it happens electronically in a fraction of a second. The speed changed. The matching did not.

Every trade has two sides, and both have to be there.

Small orders are easy

For a small order this is invisible. You buy the equivalent of a few ounces of gold at 2,431 and there is always someone on the other side. You never notice the match happening.